LINQ: How do I concatenate a list of integers into comma delimited string?

Which version of .NET? In 4.0 you can use:

string.Join(",", integerArray);

In 3.5 I would be tempted to just use:

string.Join(",", Array.ConvertAll(integerArray, i => i.ToString()));

assuming it is an array. Otherwise, either make it an array, or use StringBuilder.