Managed assembly loading algorithm

Managed assemblies are located and loaded with an algorithm that has various stages.

All managed assemblies except satellite assemblies and WinRT assemblies use the same algorithm.

When are managed assemblies loaded?

The most common mechanism to trigger a managed assembly load is a static assembly reference. These references are inserted by the compiler whenever code uses a type defined in another assembly. These assemblies are loaded (load-by-name) as needed by the runtime. The exact timing of when the static assembly references are loaded is unspecified. It can vary between runtime versions and is influenced by optimizations like inlining.

The direct use of the following APIs will also trigger loads:

API Description Active AssemblyLoadContext
AssemblyLoadContext.LoadFromAssemblyName Load-by-name The this instance.


Load from path. The this instance.
AssemblyLoadContext.LoadFromStream Load from object. The this instance.
Assembly.LoadFile Load from path in a new AssemblyLoadContext instance The new AssemblyLoadContext instance.
Assembly.LoadFrom Load from path in the AssemblyLoadContext.Default instance.

Adds an AppDomain.AssemblyResolve handler. The handler will load the assembly's dependencies from its directory.

The AssemblyLoadContext.Default instance.



Load-by-name. Inferred from caller.

Prefer AssemblyLoadContext methods.


Assembly.Load(Byte[], Byte[])

Load from object in a new AssemblyLoadContext instance. The new AssemblyLoadContext instance.

Type.GetType(String, Boolean)

Type.GetType(String, Boolean, Boolean)

Load-by-name. Inferred from caller.

Prefer Type.GetType methods with an assemblyResolver argument.

Assembly.GetType If type name describes an assembly qualified generic type, trigger a Load-by-name. Inferred from caller.

Prefer Type.GetType when using assembly qualified type names.

Activator.CreateInstance(String, String)

Activator.CreateInstance(String, String, Object[])

Activator.CreateInstance(String, String, Boolean, BindingFlags, Binder, Object[], CultureInfo, Object[])

Load-by-name. Inferred from caller.

Prefer Activator.CreateInstance methods taking a Type argument.


The following algorithm describes how the runtime loads a managed assembly.

  1. Determine the active AssemblyLoadContext.

  2. For the Load-by-name methods, the active AssemblyLoadContext loads the assembly in the following priority order:

  3. For the other types of loads, the active AssemblyLoadContext loads the assembly in the following priority order:

    • Check its cache-by-name.
    • Load from the specified path or raw assembly object. If an assembly is newly loaded, a reference is added to the active AssemblyLoadContext instance's cache-by-name.
  4. In either case, if an assembly is newly loaded, then the AppDomain.AssemblyLoad event is raised.