Conflicts between regular armies and various groups of insurgents, fighting for a range of causes, are some of the most protracted and extensive military crises to have emerged in recent years. The introduction provides a point on which the five major historical examples that follow may be compared and contrasted. Similarities and differences between some of the more important episodes from this century are highlighted; similarities such as the role of intelligence, the value of police work and the necesity of expert political assessment and differences such as the factors of time or geography, or more strategically, success or failure.