While not disputing the claim that the word ‘dialectic’ has many meanings, it is argued that there exists in the diversity a unity which is expressed as a conception of development that possesses four interrelated features: qualitative transformation, process, opposition, and internal necessity. The understanding of dialectic has evolved from ancient times to the present, with materialist dialectic representing the most advanced form. Some conclusions for a dialectical psychology are drawn from the work of Vygotsky and Leont’ev.