Experimental studies are characterized by assessing the effect of one or more interventions, usually comparatively with other intervention, or placebo; and the prospective nature of data collection and follow-up. Clustered under this denomination, a variety of designs, among which are the quasiexperimental studies (QES), which are characterized particularly by the absence of randomization. The aim of this manuscript is to report the basic principles, types, characteristics and strategies for conducting QES.