Decompiler are very useful when you don’t have your source and if you have only the assembly (dll).at this time we can decompiler and get the source .there are different decompiler available but most of them are too costly .in our .net framework itself we have decompiler Ildasm.exe but the output will be in MSIL, Hence we are going for third party decompiler. In that way reflector is very useful and freeware .few of the articles which I gone through are http://aspnet.4guysfromrolla.com/articles/080404-1.aspx