Reviews & synthesizes the state of research on a variety of meditation practices (MP), incl.: the specific MP examined; the research designs employed & the conditions & outcomes examined; the efficacy & effectiveness of different MP for the 3 most studied conditions; the role of effect modifiers on outcomes; & the effects of meditation on physiological & neuropsychological outcomes. Conclusions: scientific research on MP does not have a common theoretical perspective & is characterized by poor methodological quality. Firm conclusions on the effects of MP in healthcare cannot be drawn based on the available evidence. Future research on MP must be more rigorous in the design & execution of studies & in the analysis & reporting of results. Illus.