What’s the main difference between int.Parse() and Convert.ToInt32

Question

If you’ve got a string, and you expect it to always be an integer (say, if some web service is handing you an integer in string format), you’d use Int32.Parse().
If you’re collecting input from a user, you’d generally use Int32.TryParse(), since it allows you more fine-grained control over the situation when the user enters invalid input.
Convert.ToInt32() takes an object as its argument. (See Chris S’s answer for how it works)

Convert.ToInt32() also does not throw ArgumentNullException when its argument is null the way Int32.Parse() does. That also means that Convert.ToInt32() is probably a wee bit slower than Int32.Parse(), though in practice, unless you’re doing a very large number of iterations in a loop, you’ll never notice it.