Аннотация:The true belief components of Plato’s tripartite definition of knowledge as justified true belief are represented in formal epistemology by modal logic and its possible worlds semantics. At the same time, the justification component of Plato’s definition did not have a formal representation. This paper introduces the notion of justification into formal epistemology. Epistemic logic with justification, along with the usual knowledge operator □F (F is known), contains assertions t:F (t is a justification for F). We suggest an epistemic semantics which augments Kripke models with a natural Fitting-style treatment of justification assertions t:F. Completeness and some new specific properties of basic systems of epistemic logic with justification are established.