diff --git a/crates/engine/src/catalogue.rs b/crates/engine/src/catalogue.rs
index de74bbe..186efe0 100644
--- a/crates/engine/src/catalogue.rs
+++ b/crates/engine/src/catalogue.rs
@@ -414,7 +414,14 @@ pub static CATALOGUE: &[Capability] = &[
         "Kinematic or distributing coupling of a set to a reference point",
         &["model.coupling.edit", "model.coupling.delete"],
     ),
-    soon("interaction.tie", "Tie", Interactions, "Constraints", "M7", "Tie non-matching meshes together"),
+    ready_more(
+        "interaction.tie",
+        "Tie",
+        Interactions,
+        "Constraints",
+        "Tie non-matching meshes together (dual mortar constraints)",
+        &["interaction.tie.edit", "interaction.tie.delete"],
+    ),
     ready_more(
         "interaction.contact.general",
         "General Contact",
diff --git a/crates/engine/src/cmd/contact.rs b/crates/engine/src/cmd/contact.rs
index ddf29ba..1086be7 100644
--- a/crates/engine/src/cmd/contact.rs
+++ b/crates/engine/src/cmd/contact.rs
@@ -1,5 +1,5 @@
 //! `interaction.contact.*`: contact definitions (pairs of surfaces, general contact) and the
-//! search for surfaces that touch.
+//! search for surfaces that touch; `interaction.tie*`: ties between non-matching meshes.
 //!
 //! A contact's surfaces are sets of element faces ([`fieldcraft_model::contact`]). The commands
 //! take the friction, penalty scale and initial-penetration choice of the model's form; `edit`
@@ -14,7 +14,7 @@
 use std::collections::BTreeMap;
 
 use fieldcraft_fem::contact::{Grid, bounds, closest_point};
-use fieldcraft_model::{Contact, ContactSurfaces, ElementFace, Friction, InitialPenetration, Model, Set};
+use fieldcraft_model::{Contact, ContactSurfaces, ElementFace, Friction, InitialPenetration, Model, Set, Tie};
 use serde_json::{Value, json};
 
 use super::{name, opt};
@@ -102,6 +102,53 @@ pub const DELETE: CommandSpec = CommandSpec {
     },
 };
 
+/// A tie from the parameters.
+fn tie(p: &Value) -> Result<Tie> {
+    Ok(Tie {
+        main: text(p, "main")?.to_string(),
+        secondary: text(p, "secondary")?.to_string(),
+        position_tolerance: opt::<f64>(p, "position_tolerance")?,
+    })
+}
+
+pub const TIE: CommandSpec = CommandSpec {
+    id: "interaction.tie",
+    label: "Tie",
+    params: r#"{"name": "glue", "main": "plate" (a set of element faces), "secondary": "rib" (another), "position_tolerance": 0.1 (optional: how far a secondary node may lie from the main surface and still be tied; default half the main element's thickness)} — bonds the secondary surface to the main one across non-matching meshes: each secondary node follows the main surface under it (dual mortar constraints in the implicit analyses; a constant stress crosses the tie exactly); fails if the name is taken"#,
+    form: Some(super::forms::TIE),
+    kind: CommandKind::Model,
+    run: |s: &mut Session, p: &Value| {
+        let n = name(p)?;
+        s.model.add_tie(n, tie(p)?)?;
+        Ok(json!({"name": n}))
+    },
+};
+
+pub const TIE_EDIT: CommandSpec = CommandSpec {
+    id: "interaction.tie.edit",
+    label: "Edit Tie",
+    params: r#"{"name": "glue", "main": "plate", "secondary": "rib", "position_tolerance": 0.1} — replaces the tie of that name (see interaction.tie)"#,
+    form: Some(super::forms::TIE_EDIT),
+    kind: CommandKind::Model,
+    run: |s: &mut Session, p: &Value| {
+        let n = name(p)?;
+        s.model.replace_tie(n, tie(p)?)?;
+        Ok(json!({"name": n}))
+    },
+};
+
+pub const TIE_DELETE: CommandSpec = CommandSpec {
+    id: "interaction.tie.delete",
+    label: "Delete Tie",
+    params: r#"{"name": "glue"}"#,
+    form: Some(super::forms::TIE_DELETE),
+    kind: CommandKind::Model,
+    run: |s: &mut Session, p: &Value| {
+        s.model.remove_tie(name(p)?)?;
+        Ok(Value::Null)
+    },
+};
+
 pub const FIND: CommandSpec = CommandSpec {
     id: "interaction.contact.find",
     label: "Find Contacts",
@@ -334,6 +381,32 @@ mod tests {
         assert!(s.model.contacts().is_empty());
     }
 
+    #[test]
+    fn ties_are_created_edited_and_deleted() {
+        let mut s = Session::default();
+        stacked(&mut s);
+        s.execute("model.set.create", &json!({"name": "a", "faces": [{"element": 5, "face": 2}]})).unwrap();
+        s.execute("model.set.create", &json!({"name": "b", "faces": [{"element": 9, "face": 1}]})).unwrap();
+        s.execute("interaction.tie", &json!({"name": "glue", "main": "a", "secondary": "b"})).unwrap();
+        assert_eq!(s.model.tie("glue"), Some(&Tie::new("a", "b")));
+        for bad in [
+            json!({"name": "glue", "main": "a", "secondary": "b"}),
+            json!({"name": "x", "main": "a", "secondary": "a"}),
+            json!({"name": "x", "main": "a", "secondary": "nope"}),
+            json!({"name": "x", "main": "a", "secondary": "b", "position_tolerance": -1}),
+            json!({"name": "x", "main": "a", "secondary": "b", "position_tolerance": "far"}),
+            json!({"name": "x", "main": 3, "secondary": "b"}),
+        ] {
+            assert!(s.execute("interaction.tie", &bad).is_err(), "{bad}");
+        }
+        s.execute("interaction.tie.edit", &json!({"name": "glue", "main": "b", "secondary": "a", "position_tolerance": 0.01})).unwrap();
+        assert_eq!(s.model.tie("glue").and_then(|t| t.position_tolerance), Some(0.01));
+        assert!(s.execute("interaction.tie.edit", &json!({"name": "nope", "main": "a", "secondary": "b"})).is_err());
+        assert!(s.execute("model.set.delete", &json!({"name": "a"})).unwrap_err().to_string().contains("tie `glue`"));
+        s.execute("interaction.tie.delete", &json!({"name": "glue"})).unwrap();
+        assert!(s.model.ties().is_empty() && s.execute("interaction.tie.delete", &json!({"name": "glue"})).is_err());
+    }
+
     #[test]
     fn find_reports_and_creates_the_touching_parts() {
         let mut s = Session::default();
diff --git a/crates/engine/src/cmd/forms.rs b/crates/engine/src/cmd/forms.rs
index 13b2404..704c67f 100644
--- a/crates/engine/src/cmd/forms.rs
+++ b/crates/engine/src/cmd/forms.rs
@@ -31,6 +31,7 @@ pub const BOUNDARY_CONDITION_DELETE: &[Field] = existing!("Boundary condition",
 pub const LOAD_DELETE: &[Field] = existing!("Load", C::Load);
 pub const FLUID_DOMAIN_DELETE: &[Field] = existing!("Fluid domain", C::FluidDomain);
 pub const CONTACT_DELETE: &[Field] = existing!("Contact", C::Contact);
+pub const TIE_DELETE: &[Field] = existing!("Tie", C::Tie);
 pub const STEP_DELETE: &[Field] = existing!("Step", C::Step);
 pub const SET_RESOLVE: &[Field] = existing!("Set", C::Set);
 
@@ -614,6 +615,18 @@ pub const CONTACT_EDIT: &[Field] = &[
     PENALTY,
     PENETRATION,
 ];
+pub const TIE: &[Field] = &[
+    NAME,
+    reference("main", "Main surface", C::Set).req(),
+    reference("secondary", "Secondary surface", C::Set).req(),
+    positive("position_tolerance", "Position tolerance", D::Length).hint("half the main element's thickness"),
+];
+pub const TIE_EDIT: &[Field] = &[
+    reference("name", "Tie", C::Tie).req(),
+    reference("main", "Main surface", C::Set).req(),
+    reference("secondary", "Secondary surface", C::Set).req(),
+    positive("position_tolerance", "Position tolerance", D::Length).hint("half the main element's thickness"),
+];
 pub const CONTACT_FIND: &[Field] = &[
     positive("tolerance", "Tolerance", D::Length).hint("a tenth of the mean face size"),
     flag("create", "Create pairs").def("false"),
diff --git a/crates/engine/src/cmd/mod.rs b/crates/engine/src/cmd/mod.rs
index 2d104e9..94a136a 100644
--- a/crates/engine/src/cmd/mod.rs
+++ b/crates/engine/src/cmd/mod.rs
@@ -74,6 +74,9 @@ pub static ALL: &[CommandSpec] = &[
     contact::EDIT,
     contact::DELETE,
     contact::FIND,
+    contact::TIE,
+    contact::TIE_EDIT,
+    contact::TIE_DELETE,
     define::MASS_CREATE,
     define::MASS_EDIT,
     define::MASS_DELETE,
diff --git a/crates/engine/src/schema.rs b/crates/engine/src/schema.rs
index b0d3245..5fa157c 100644
--- a/crates/engine/src/schema.rs
+++ b/crates/engine/src/schema.rs
@@ -107,6 +107,7 @@ pub enum Collection {
     ReferencePoint,
     Coupling,
     Contact,
+    Tie,
     Mass,
     Spring,
     BoundaryCondition,
@@ -128,6 +129,7 @@ impl Collection {
             Collection::ReferencePoint => "reference point",
             Collection::Coupling => "coupling",
             Collection::Contact => "contact",
+            Collection::Tie => "tie",
             Collection::Mass => "point mass",
             Collection::Spring => "spring",
             Collection::BoundaryCondition => "boundary condition",
@@ -151,6 +153,7 @@ impl Session {
             Collection::ReferencePoint => Box::new(m.reference_points().keys().map(String::as_str)),
             Collection::Coupling => Box::new(m.couplings().keys().map(String::as_str)),
             Collection::Contact => Box::new(m.contacts().keys().map(String::as_str)),
+            Collection::Tie => Box::new(m.ties().keys().map(String::as_str)),
             Collection::Mass => Box::new(m.masses().keys().map(String::as_str)),
             Collection::Spring => Box::new(m.springs().keys().map(String::as_str)),
             Collection::BoundaryCondition => Box::new(m.boundary_conditions().keys().map(String::as_str)),
diff --git a/docs/features.md b/docs/features.md
index 3f28f88..55958fa 100644
--- a/docs/features.md
+++ b/docs/features.md
@@ -6,7 +6,7 @@ Every entry is a toolbar button. **Ready** entries run their command; **coming s
 shown greyed with the roadmap milestone that brings them (ROADMAP.md). Scripts, the command line,
 the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 
-59 ready, 45 coming soon.
+60 ready, 44 coming soon.
 
 ## Geometry
 
@@ -102,7 +102,7 @@ the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 |---|---|---|---|
 | Constraints | Reference Point — A reference point for couplings, loads and boundary conditions | ready | `model.reference_point.create`, `model.reference_point.edit`, `model.reference_point.delete` |
 | Constraints | Coupling — Kinematic or distributing coupling of a set to a reference point | ready | `model.coupling.create`, `model.coupling.edit`, `model.coupling.delete` |
-| Constraints | Tie — Tie non-matching meshes together | coming soon (M7) |  |
+| Constraints | Tie — Tie non-matching meshes together (dual mortar constraints) | ready | `interaction.tie`, `interaction.tie.edit`, `interaction.tie.delete` |
 | Contact | General Contact — Contact between everything that may touch, or self contact of a surface, with friction (explicit dynamics) | ready | `interaction.contact.general`, `interaction.contact.edit`, `interaction.contact.delete` |
 | Contact | Contact Pair — Contact between two surfaces: with friction in explicit dynamics, mortar contact with friction in nonlinear static steps | ready | `interaction.contact.pair`, `interaction.contact.edit`, `interaction.contact.delete` |
 | Contact | Find Contacts — Find the parts of the mesh that touch, and make contact pairs of them | ready | `interaction.contact.find` |