The term meditation is ill-defined. Even meditation researchers mean different things when they talk about meditation, and sometimes use the term mindfulness synonymously. In fact, there are hundreds of sometimes widely differing meditation techniques, and mindfulness techniques (of different varieties) are part of them.

People meditate for quite different reasons. Traditionally there is just one reason to meditate, variously termed enlightenment, liberation, awakening, or something similar. However, many contemporary meditators meditate for therapeutic reasons (although meditation cannot replace psychotherapy). Others want to find out more about themselves, to improve their cognitive skills, or just to enjoy life more.

Meditation comes with different backgrounds. Traditionally, meditation has always been closely connected with religion (of one or other sorts), including its ethical aspects. This sometimes creates a problem in that traditional (or new) belief systems may obstruct meditators' openness to scientific scrutiny. It is still unclear how important a religious (or ideological) background is, but at least the ethical aspects might play some role.

There is huge variation in the effects of meditation. Although meditation overall has almost universally beneficial effects, in some cases it can be harmful. Research on the question of which kind of meditation has which effects, for which kinds of persons with which kinds of aims, and in which context, is only in its nascent stage. The existing evidence indicates that not everybody benefits equally from every meditation technique, and that the effects of meditation may be strongly influenced by meditators' reasons to meditate, their current situation, and their personalities. 

Research is still largely conducted without a sound theoretical basis. The bulk of meditation research still examines the question of whether meditation (often not differentiated) has an effect on X, where X can refer to a huge variety of psychological variables. As yet, there is no comprehensive theory of meditation but there are several traditional (Buddhist and Hindu) theoretical approaches as well as Western frameworks. However, hypotheses derived from these theoretical backgrounds are rarely examined in meditation research.

Meditation can be used as a research technique. A promising approach to meditation research, but one rarely used so far, is to train researchers to observe their “inner life” by having them meditate. There is evidence that meditators have an improved ability to perceive what is going on in themselves. Experienced meditators, especially if they are also researchers, might be able to advance our theories of cognition and consciousness considerably.

In summary, meditation research sees itself confronted by many more questions than answers. My book provides some answers, but one of its main aims is actually to make the questions we need to ask more explicit. This is the only way to eventually arrive at a better understanding of this fascinating topic.