I have a little over 5 years (as of February 2015) of experience with League of Legends and I believe that the pure amount of knowledge and experience I've gained over this period of time gives me the credibility to make this guide.
This furry midget is a pretty underrated champion whose popularity peaked somewhere during Season 2 when going AP mid, AP top and having both build the old Will of the Ancients (which used to have an aura that gave surrounding teammates spell vamp, and not just yourself) was all the jazz. He also made a resurgence a bit in Season 3 when Koreans tried him with Blade of the Ruined King , but eventually fell out of favor once again afterwards.
The original goal of this guide was to present a somewhat-tanky version of Kennen who would not serve as only a good source of CC, but as well as a source of initiation and zoning power while being fairly durable. After dabbling with Kennen some more throughout Season 4 and now Season 5, I have come to a realization that a more typical-AP build for Kennen works fine and may be preferable to the lot of you as you also deal damage.
While this guide is assuming that Kennen is to be played top, he can still do okay in the mid lane, but for reasons explained later I will clarify why I believe he is better served top.