diff --git a/Cargo.lock b/Cargo.lock
index f992d2647..99fe88d7b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "ahash"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "739f4a8db6605981345c5654f3a85b056ce52f37a39d34da03f25bf2151ea16e"
+
 [[package]]
 name = "aho-corasick"
 version = "0.7.18"
@@ -11,12 +17,6 @@ dependencies = [
  "memchr",
 ]
 
-[[package]]
-name = "arrayvec"
-version = "0.5.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
-
 [[package]]
 name = "assert_cmd"
 version = "2.0.4"
@@ -37,6 +37,17 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b34d609dfbaf33d6889b2b7106d3ca345eacad44200913df5ba02bfd31d2ba9"
 
+[[package]]
+name = "async-trait"
+version = "0.1.52"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "061a7acccaa286c011ddc30970520b98fa40e00c9d644633fb26b5fc63a265e3"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "atty"
 version = "0.2.14"
@@ -65,6 +76,12 @@ dependencies = [
  "rand",
 ]
 
+[[package]]
+name = "base64"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "904dfeac50f3cdaba28fc6f57fdcddb75f49ed61346676a78c4ffe55877802fd"
+
 [[package]]
 name = "bitflags"
 version = "1.2.1"
@@ -119,7 +136,7 @@ dependencies = [
  "lazy_static",
  "memchr",
  "regex-automata",
- "serde 1.0.126",
+ "serde",
 ]
 
 [[package]]
@@ -178,7 +195,7 @@ checksum = "670ad68c9088c2a963aaa298cb369688cf3f9465ce5e2d4ca10e6e0098a1ce73"
 dependencies = [
  "libc",
  "num-integer",
- "num-traits 0.2.14",
+ "num-traits",
  "time",
  "winapi",
 ]
@@ -231,15 +248,18 @@ dependencies = [
 
 [[package]]
 name = "config"
-version = "0.11.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b1b9d958c2b1368a663f05538fc1b5975adce1e19f435acceae987aceeeb369"
+checksum = "54ad70579325f1a38ea4c13412b82241c5900700a69785d73e2736bd65a33f86"
 dependencies = [
+ "async-trait",
+ "json5",
  "lazy_static",
  "nom",
+ "pathdiff",
+ "ron",
  "rust-ini",
- "serde 1.0.126",
- "serde-hjson",
+ "serde",
  "serde_json",
  "toml",
  "yaml-rust",
@@ -271,12 +291,12 @@ dependencies = [
  "csv",
  "itertools",
  "lazy_static",
- "num-traits 0.2.14",
+ "num-traits",
  "oorandom",
  "plotters",
  "rayon",
  "regex",
- "serde 1.0.126",
+ "serde",
  "serde_cbor",
  "serde_derive",
  "serde_json",
@@ -367,7 +387,7 @@ dependencies = [
  "csv-core",
  "itoa 0.4.7",
  "ryu",
- "serde 1.0.126",
+ "serde",
 ]
 
 [[package]]
@@ -425,6 +445,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "dlv-list"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68df3f2b690c1b86e65ef7830956aededf3cb0a16f898f79b9a6f421a7b6211b"
+dependencies = [
+ "rand",
+]
+
 [[package]]
 name = "doc-comment"
 version = "0.3.3"
@@ -464,7 +493,7 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "98de4bbd547a563b716d8dfa9aad1cb19bfab00f4fa09a6a4ed21dbcf44ce9c4"
 dependencies = [
- "num-traits 0.2.14",
+ "num-traits",
 ]
 
 [[package]]
@@ -528,6 +557,15 @@ version = "1.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "62aca2aba2d62b4a7f5b33f3712cb1b0692779a56fb510499d5c0aa594daeaf3"
 
+[[package]]
+name = "hashbrown"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
+dependencies = [
+ "ahash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.11.2"
@@ -567,7 +605,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bc633605454125dec4b66843673f01c7df2b89479b32e0ed634e43a91cff62a5"
 dependencies = [
  "autocfg",
- "hashbrown",
+ "hashbrown 0.11.2",
 ]
 
 [[package]]
@@ -587,7 +625,7 @@ checksum = "30a7e1911532a662f6b08b68f884080850f2fd9544963c3ab23a5af42bda1eac"
 dependencies = [
  "console",
  "once_cell",
- "serde 1.0.126",
+ "serde",
  "serde_json",
  "serde_yaml",
  "similar",
@@ -641,6 +679,17 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "json5"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96b0db21af676c1ce64250b5f40f3ce2cf27e4e47cb91ed91eb6fe9350b430c1"
+dependencies = [
+ "pest",
+ "pest_derive",
+ "serde",
+]
+
 [[package]]
 name = "jujutsu"
 version = "0.3.3"
@@ -711,19 +760,6 @@ version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
-[[package]]
-name = "lexical-core"
-version = "0.7.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6607c62aa161d23d17a9072cc5da0be67cdfc89d3afb1e8d9c842bebc2525ffe"
-dependencies = [
- "arrayvec",
- "bitflags",
- "cfg-if",
- "ryu",
- "static_assertions",
-]
-
 [[package]]
 name = "libc"
 version = "0.2.97"
@@ -813,14 +849,19 @@ dependencies = [
 ]
 
 [[package]]
-name = "nom"
-version = "5.1.2"
+name = "minimal-lexical"
+version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ffb4262d26ed83a1c0a33a38fe2bb15797329c85770da05e6b828ddb782627af"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8903e5a29a317527874d0402f867152a3d21c908bb0b933e416c65e301d4c36"
 dependencies = [
- "lexical-core",
  "memchr",
- "version_check",
+ "minimal-lexical",
 ]
 
 [[package]]
@@ -836,16 +877,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2cc698a63b549a70bc047073d2949cce27cd1c7b0a4a862d08a8031bc2801db"
 dependencies = [
  "autocfg",
- "num-traits 0.2.14",
-]
-
-[[package]]
-name = "num-traits"
-version = "0.1.43"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "92e5113e9fd4cc14ded8e499429f396a20f98c772a47cc8622a736e1ec843c31"
-dependencies = [
- "num-traits 0.2.14",
+ "num-traits",
 ]
 
 [[package]]
@@ -914,6 +946,16 @@ dependencies = [
  "vcpkg",
 ]
 
+[[package]]
+name = "ordered-multimap"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1c672c7ad9ec066e428c00eb917124a06f08db19e2584de982cc34b1f4c12485"
+dependencies = [
+ "dlv-list",
+ "hashbrown 0.9.1",
+]
+
 [[package]]
 name = "os_str_bytes"
 version = "6.0.0"
@@ -923,6 +965,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "pathdiff"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8835116a5c179084a830efb3adc117ab007512b535bc1a21c991d3b32a6b44dd"
+
 [[package]]
 name = "percent-encoding"
 version = "2.1.0"
@@ -984,7 +1032,7 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32a3fd9ec30b9749ce28cd91f255d569591cdf937fe280c312143e3c4bad6f2a"
 dependencies = [
- "num-traits 0.2.14",
+ "num-traits",
  "plotters-backend",
  "plotters-svg",
  "wasm-bindgen",
@@ -1225,10 +1273,25 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b833d8d034ea094b1ea68aa6d5c740e0d04bad9d16568d08ba6f76823a114316"
 
 [[package]]
-name = "rust-ini"
-version = "0.13.0"
+name = "ron"
+version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3e52c148ef37f8c375d49d5a73aa70713125b7f19095948a923f80afdeb22ec2"
+checksum = "1b861ecaade43ac97886a512b360d01d66be9f41f3c61088b42cedf92e03d678"
+dependencies = [
+ "base64",
+ "bitflags",
+ "serde",
+]
+
+[[package]]
+name = "rust-ini"
+version = "0.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63471c4aa97a1cf8332a5f97709a79a4234698de6a1f5087faf66f2dae810e22"
+dependencies = [
+ "cfg-if",
+ "ordered-multimap",
+]
 
 [[package]]
 name = "rustc_version"
@@ -1278,12 +1341,6 @@ dependencies = [
  "pest",
 ]
 
-[[package]]
-name = "serde"
-version = "0.8.23"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9dad3f759919b92c3068c696c15c3d17238234498bbdcc80f2c469606f948ac8"
-
 [[package]]
 name = "serde"
 version = "1.0.126"
@@ -1293,18 +1350,6 @@ dependencies = [
  "serde_derive",
 ]
 
-[[package]]
-name = "serde-hjson"
-version = "0.9.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6a3a4e0ea8a88553209f6cc6cfe8724ecad22e1acf372793c27d995290fe74f8"
-dependencies = [
- "lazy_static",
- "num-traits 0.1.43",
- "regex",
- "serde 0.8.23",
-]
-
 [[package]]
 name = "serde_cbor"
 version = "0.11.1"
@@ -1312,7 +1357,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e18acfa2f90e8b735b2836ab8d538de304cbb6729a7360729ea5a895d15a622"
 dependencies = [
  "half",
- "serde 1.0.126",
+ "serde",
 ]
 
 [[package]]
@@ -1334,7 +1379,7 @@ checksum = "8e8d9fa5c3b304765ce1fd9c4c8a3de2c8db365a5b91be52f186efc675681d95"
 dependencies = [
  "itoa 1.0.1",
  "ryu",
- "serde 1.0.126",
+ "serde",
 ]
 
 [[package]]
@@ -1345,7 +1390,7 @@ checksum = "a4a521f2940385c165a24ee286aa8599633d162077a54bdcae2a6fd5a7bfa7a0"
 dependencies = [
  "indexmap",
  "ryu",
- "serde 1.0.126",
+ "serde",
  "yaml-rust",
 ]
 
@@ -1373,12 +1418,6 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f67ad224767faa3c7d8b6d91985b78e70a1324408abcb1cfcc2be4c06bc06043"
 
-[[package]]
-name = "static_assertions"
-version = "1.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
-
 [[package]]
 name = "strsim"
 version = "0.10.0"
@@ -1511,7 +1550,7 @@ version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "be4d6b5f19ff7664e8c98d03e2139cb510db9b0a60b55f8e8709b689d939b6bc"
 dependencies = [
- "serde 1.0.126",
+ "serde",
  "serde_json",
 ]
 
@@ -1536,7 +1575,7 @@ version = "0.5.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a31142970826733df8241ef35dc040ef98c679ab14d7c3e54d827099b3acecaa"
 dependencies = [
- "serde 1.0.126",
+ "serde",
 ]
 
 [[package]]
diff --git a/Cargo.toml b/Cargo.toml
index 3b0b2b818..096ef82c0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,7 +30,7 @@ chrono = "0.4.19"
 clap = { version = "3.1.6", features = ["cargo"] }
 clap_complete = "3.1.1"
 clap_mangen = "0.1"
-config = "0.11.0"
+config = "0.12.0"
 criterion = "0.3.5"
 git2 = "0.14.2"
 hex = "0.4.3"
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index e923490ea..c1ad95752 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -22,7 +22,7 @@ blake2 = "0.10.4"
 bytes = "1.1.0"
 byteorder = "1.4.3"
 chrono = "0.4.19"
-config = "0.11.0"
+config = "0.12.0"
 dirs = "4.0.0"
 git2 = "0.14.2"
 hex = "0.4.3"
diff --git a/lib/src/settings.rs b/lib/src/settings.rs
index 98713fd10..26909a57d 100644
--- a/lib/src/settings.rs
+++ b/lib/src/settings.rs
@@ -35,7 +35,7 @@ const TOO_MUCH_CONFIG_ERROR: &str =
 
 impl UserSettings {
     pub fn from_config(config: config::Config) -> Self {
-        let timestamp = match config.get_str("user.timestamp") {
+        let timestamp = match config.get_string("user.timestamp") {
             Ok(timestamp_str) => match DateTime::parse_from_rfc3339(&timestamp_str) {
                 Ok(datetime) => Some(Timestamp::from_datetime(datetime)),
                 Err(_) => None,
@@ -46,18 +46,18 @@ impl UserSettings {
     }
 
     pub fn for_user() -> Result<Self, config::ConfigError> {
-        let mut config = config::Config::new();
+        let mut config_builder = config::Config::builder();
 
         let loaded_from_config_dir = match dirs::config_dir() {
             None => false,
             Some(config_dir) => {
                 let p = config_dir.join("jj/config.toml");
                 let exists = p.exists();
-                config.merge(
+                config_builder = config_builder.add_source(
                     config::File::from(p)
                         .required(false)
                         .format(config::FileFormat::Toml),
-                )?;
+                );
                 exists
             }
         };
@@ -71,48 +71,52 @@ impl UserSettings {
                     TOO_MUCH_CONFIG_ERROR.to_string(),
                 ));
             }
-            config.merge(
+            config_builder = config_builder.add_source(
                 config::File::from(p)
                     .required(false)
                     .format(config::FileFormat::Toml),
-            )?;
+            );
         }
 
-        let mut env_config = config::Config::new();
+        // TODO: Make the config from environment a separate source instead? Seems
+        // cleaner to separate it like that, especially if the config::Config instance
+        // can keep track of where the config comes from then (it doesn't seem like it
+        // can, however - we don't give a name or anything to the Config object).
         if let Ok(value) = env::var("JJ_USER") {
-            env_config.set("user.name", value)?;
+            config_builder = config_builder.set_override("user.name", value)?;
         }
         if let Ok(value) = env::var("JJ_EMAIL") {
-            env_config.set("user.email", value)?;
+            config_builder = config_builder.set_override("user.email", value)?;
         }
         if let Ok(value) = env::var("JJ_TIMESTAMP") {
-            env_config.set("user.timestamp", value)?;
+            config_builder = config_builder.set_override("user.timestamp", value)?;
         }
-        config.merge(env_config)?;
 
+        let config = config_builder.build()?;
         Ok(Self::from_config(config))
     }
 
     pub fn with_repo(&self, repo_path: &Path) -> Result<RepoSettings, config::ConfigError> {
-        let mut config = self.config.clone();
-        config.merge(
-            config::File::from(repo_path.join("config"))
-                .required(false)
-                .format(config::FileFormat::Toml),
-        )?;
-
+        let config = config::Config::builder()
+            .add_source(self.config.clone())
+            .add_source(
+                config::File::from(repo_path.join("config"))
+                    .required(false)
+                    .format(config::FileFormat::Toml),
+            )
+            .build()?;
         Ok(RepoSettings { _config: config })
     }
 
     pub fn user_name(&self) -> String {
         self.config
-            .get_str("user.name")
+            .get_string("user.name")
             .unwrap_or_else(|_| "(no name configured)".to_string())
     }
 
     pub fn user_email(&self) -> String {
         self.config
-            .get_str("user.email")
+            .get_string("user.email")
             .unwrap_or_else(|_| "(no email configured)".to_string())
     }
 
diff --git a/lib/src/testutils.rs b/lib/src/testutils.rs
index ee8438fff..dd1d44e92 100644
--- a/lib/src/testutils.rs
+++ b/lib/src/testutils.rs
@@ -42,9 +42,13 @@ pub fn new_user_home() -> TempDir {
 }
 
 pub fn user_settings() -> UserSettings {
-    let mut config = config::Config::new();
-    config.set("user.name", "Test User").unwrap();
-    config.set("user.email", "test.user@example.com").unwrap();
+    let config = config::Config::builder()
+        .set_override("user.name", "Test User")
+        .unwrap()
+        .set_override("user.email", "test.user@example.com")
+        .unwrap()
+        .build()
+        .unwrap();
     UserSettings::from_config(config)
 }
 
diff --git a/lib/tests/test_commit_builder.rs b/lib/tests/test_commit_builder.rs
index 4ca879928..f3d8e7790 100644
--- a/lib/tests/test_commit_builder.rs
+++ b/lib/tests/test_commit_builder.rs
@@ -99,10 +99,12 @@ fn test_rewrite(use_git: bool) {
         ],
     );
 
-    let mut config = config::Config::new();
-    config.set("user.name", "Rewrite User").unwrap();
-    config
-        .set("user.email", "rewrite.user@example.com")
+    let config = config::Config::builder()
+        .set_override("user.name", "Rewrite User")
+        .unwrap()
+        .set_override("user.email", "rewrite.user@example.com")
+        .unwrap()
+        .build()
         .unwrap();
     let rewrite_settings = UserSettings::from_config(config);
     let mut tx = repo.start_transaction("test");
diff --git a/lib/tests/test_init.rs b/lib/tests/test_init.rs
index 966febae4..873c33987 100644
--- a/lib/tests/test_init.rs
+++ b/lib/tests/test_init.rs
@@ -71,7 +71,7 @@ fn test_init_external_git() {
 #[test_case(true ; "git backend")]
 fn test_init_no_config_set(use_git: bool) {
     // Test that we can create a repo without setting any config
-    let settings = UserSettings::from_config(config::Config::new());
+    let settings = UserSettings::from_config(config::Config::default());
     let test_workspace = testutils::init_workspace(&settings, use_git);
     let repo = &test_workspace.repo;
     let checkout_id = repo.view().get_checkout(&WorkspaceId::default()).unwrap();
diff --git a/src/commands.rs b/src/commands.rs
index 16b0861c6..f503cad37 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -2129,7 +2129,7 @@ fn show_diff(
         } else if args.is_present("color-words") {
             Format::ColorWords
         } else {
-            match ui.settings().config().get_str("diff.format") {
+            match ui.settings().config().get_string("diff.format") {
                 Ok(value) if &value == "summary" => Format::Summary,
                 Ok(value) if &value == "git" => Format::Git,
                 Ok(value) if &value == "color-words" => Format::ColorWords,
@@ -2709,7 +2709,7 @@ fn log_template(settings: &UserSettings) -> String {
             )"#;
     settings
         .config()
-        .get_str("template.log.graph")
+        .get_string("template.log.graph")
         .unwrap_or_else(|_| String::from(default_template))
 }
 
@@ -4545,7 +4545,7 @@ fn resolve_alias(ui: &mut Ui, args: Vec<String>) -> Vec<String> {
         {
             let mut resolved_args = vec![args[0].clone()];
             for arg in alias_definition {
-                match arg.into_str() {
+                match arg.into_string() {
                     Ok(string_arg) => resolved_args.push(string_arg),
                     Err(err) => {
                         ui.write_error(&format!(
diff --git a/src/diff_edit.rs b/src/diff_edit.rs
index 35e0ad678..af7e35ea6 100644
--- a/src/diff_edit.rs
+++ b/src/diff_edit.rs
@@ -133,7 +133,7 @@ pub fn edit_diff(
     // best one here.
     let editor_binary = settings
         .config()
-        .get_str("ui.diff-editor")
+        .get_string("ui.diff-editor")
         .unwrap_or_else(|_| "meld".to_string());
     // Start a diff editor on the two directories.
     let exit_status = Command::new(&editor_binary)
diff --git a/src/ui.rs b/src/ui.rs
index 33d680be3..b4f620a91 100644
--- a/src/ui.rs
+++ b/src/ui.rs
@@ -67,7 +67,7 @@ impl<'stdout> Ui<'stdout> {
         let stdout: Box<dyn Write + 'static> = Box::new(io::stdout());
         let color_setting = settings
             .config()
-            .get_str("ui.color")
+            .get_string("ui.color")
             .unwrap_or_else(|_| "auto".to_string());
         let color = match color_setting.as_str() {
             "always" => true,
@@ -122,7 +122,7 @@ impl<'stdout> Ui<'stdout> {
         let template_string = self
             .settings
             .config()
-            .get_str("template.commit_summary")
+            .get_string("template.commit_summary")
             .unwrap_or_else(|_| {
                 String::from(
                     r#"label(if(open, "open"), commit_id.short() " " description.first_line())"#,