Let's start with the question "what is tippet?" Well, simply put , tippet is the thinnest part of your leader and is typically sold on a spool. Tippet is the one of the most critical components to fishing. There are two major groups of tippet. First is nylon tippet, sometimes called "mono." Nylon tippet floats, knots easily, and is fairly inexpensive. Nylon can go bad and expire after a few years. Nylon is best for dry flies and when fishing fast moving water. The other type of tippet is Fluorocarbon which is very abrasion resistant and sinks. Fluoro is best for nymph fishing or for wary fish, as it goes nearly invisible when it goes underwater.  Fluorocarbon also never goes bad which is why you should always make sure to hang on to the bits and pieces when building your rig. Pack it in, pack it out! For California trout fishing you should have 3x,4x,5x and 6x (rarely used except on slow moving clear water situations like Hat Creek and Fall River.) We tend to use a lot more fluorocarbon than we do nylon. I most often fish nylon when fishing streamers and large dry flies. We have fished all over the world with the tippets below and wanted for nothing.