This article explores the situation of mixed methods research (MMR) as a special strategy of combining several research methods. Changes in the conceptual frameworks since 1960th to present times concerned the concept of triangulation in the modes of research designs implementing combination and integration of qualitative and quantitative methods. The classification grounds for research design modelling proposed by J. Greene and his colleagues, A. Bryman and J. Cresswell are analyzed. Special ethical issues emerging from using of MMR are dicussed.