In the field of modern development of Private Military companies this should be your first port of call. Outlines the development of PMCs and examines the implications of these developments. Its major shortfall is that it was written before some of the major growth in Iraq in recent years. It could also look more at the implications for governments and policy makers.
A must read in the field.
Peter Mahon

This book provides an academic view of the topic (i.e., dry and sterile). Coming from an academic press (Cornell) and an academic, however, this not a surprise. The author starts with a history of the private sector in warfare during the medieval ages up to the current period, with emphasis on trend towards increasing state control (i.e., de-privitization) over time with increasing re-privatization. The later is in regard particularly to the U.S. and its overstretched (probably temporarily) forces. This is, in the author's opinion, is cause of large increase in recent expansion of privitization in the U.S. The author then discusses various aspects, mostly negative, regarding this privitization (i.e., legal status of private "troops", reliability in case of large scale combat and increase of the danger they face, etc.).

The book has two weaknesses. The first is that it does not cover the benefits of this privitazation in sufficient detail. Especially financial savings and, more importantly, the private sector filling the void in Iraq due to lack of long-term permanent U.S. public sector troops. The author needs to address the question of how else the U.S. would be able to cope without this strategy (i.e., draft?). No discussion here. Also, some perspective on other nations' attempts at privitization would be useful for purposes of perspective and comparison with U.S. How much are they privitizing vis-a-vis the U.S. and how has it affected their combat effectiveness/cost of operations. For these reasons the book receives four stars instead of five. Nevertheless, provides a good primer on the subject. Especially considering the fact that most other books have been written by journalists from a sensationalist point of view.