diff --git a/NEWS.md b/NEWS.md
index 5ce564dc..aabb825c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,11 @@
 # Molly.jl release notes
 
+## v0.4.0 - Sep 2021
+
+- Unitful.jl support is added and recommended for use, meaning numbers have physical meaning and many errors are caught. More type parameters have been added to various types to allow this. It is still possible to run simulations without units by specifying the `force_unit` and `energy_unit` arguments to `Simulation`.
+- Interaction constructors with keyword arguments are added or improved.
+- The maximum force for non-bonded interactions is removed.
+
 ## v0.3.0 - May 2021
 
 - The spelling of "neighbour" is changed to "neighbor" throughout the package. This affects `NoNeighborFinder`, `DistanceNeighborFinder`, `TreeNeighborFinder`, `find_neighbors!` and the `neighbor_finder` argument to `Simulation`.
diff --git a/Project.toml b/Project.toml
index b28f47df..d4de2e49 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "Molly"
 uuid = "aa0f7f06-fcc0-5ec4-a7f3-a573f33f9c4c"
 authors = ["Joe G Greener <jgreener@hotmail.co.uk>"]
-version = "0.3.0"
+version = "0.4.0"
 
 [deps]
 BioStructures = "de9282ab-8554-53be-b2d6-f6c222edabfc"
diff --git a/docs/src/docs.md b/docs/src/docs.md
index f7717c9c..28f74cf6 100644
--- a/docs/src/docs.md
+++ b/docs/src/docs.md
@@ -352,6 +352,7 @@ The performance overhead of using units is minimal.
 
 All your interaction types need to return the same units of force and energy or the simulation will not run.
 By default these are `kJ * mol^-1 * nm^-1` for force and `kJ * mol^-1` for energy, but this can be changed using the `force_unit` and `energy_unit` arguments to [`Simulation`](@ref).
+If you need to strip units for downstream analysis, use the `ustrip` function.
 
 ## Forces