An excellent overview to help understand the organisations and structures employed by the communist regimes in the Soviet satellite sates:
A Handbook of the Communist Security Apparatus in East Central Europe 1944-1989
by Krzysztof Persak (edit.), Łukasz Kamiński (edit.) Published by IPN Warsaw.
"The security apparatus, the "sword and shield of the party/' was a mainstay of the communist system, which let the totalitarian dicłatorship continue for so many years. The communist security apparatus in East Central Europę left tens of thousands dead, miliions incarcerated and persecuted in sundry ways. Without studying its history it is impossible to understand not only the past but also the present of this part of Europę. This book is the first attempt at a synthesis of the history of the communist security apparatus in the European countries of the Soviet błoć. Nine aułhors from six countries present the current state of research and point directions for further investigation. The publishers hope that this book will initiate a comprehensive debatę on the role of the communist security apparatus in modern history."