That and Which

Here is a review of when to use which and when to use that:

That is used without a comma when the clause that follows is essential information. For example: The book that he wrote was burned by the angry group.

Which is used, with a comma, when the following clause is incidental (filler) information. For example: The book, which was bound in leather, stayed on the shelf unread.

Key words are essential and incidental when you determine the uses of that and which.