<p>I have an Interface called <code>IStep</code> that can do some computation (See "<a href="http://steve-yegge.blogspot.com/2006/03/execution-in-kingdom-of-nouns.html" rel="nofollow noreferrer">Execution in the Kingdom of Nouns</a>"). At runtime, I want to select the appropriate implementation by class name.</p>

<pre>
// use like this:
IStep step = GetStep(sName);
</pre>

If the implementation has a parameterless constructor, you can do this using the System.Activator class. You will need to specify the assembly name in addition to the class name:
```
```
IStep step = System.Activator.CreateInstance(sAssemblyName, sClassName).Unwrap() as IStep;
```
```
http://msdn.microsoft.com/en-us/library/system.activator.createinstance.aspx