This subject is way to important to rephrase it. Therefore I will just quote it.
„Key Players is the biggest classified directory of the German games industry. It provides interesting and surprising insights into the German games market as well as more than 70 in-depth company profiles. In addition to all relevant developers and publishers, you will also find a broad selection of service partners for outsourcing, PR or localization. The Key Players book is distributed at every major industry event, including GDC.“
Unfortunately there is no 2016-2017 Version available online. They handed it out at gamescom.