Substring is the typical replacement for those other functions, though the other functions can still be used in .NET.

It sounds like you are talking about substrings of substrings, but that may not be the best way to do things. Take a look at the String.Contains and String.IndexOf methods. Contains is pretty much a replacement for InStr, while Substring can replace the Mid, Left, and Right functions. The IndexOf method is similar to Contains, but returns the location of the specified text, which allows it to be used for iterative searches, or for use with substring to work like Mid.