ABSTRACT. The problem of the extension of a real-valued function from a subset of a metric space to the entire space is treated. An extension operator preserving the modulus of continuity of a function is proposed and its properties are studied. An application to the problem of the trace of a locally Lipschitz function on a compact subset of a metric space is given.KEY WORDS: extension of a function, modulus of continuity, trace of a locally Lipschitz function.The problem of the extension of a real-valued function from a subset of a metric space to the entire space, preserving the modulus of continuity, is considered. Such problems arise in calculus and geometry (see [1, p. 220 The first class consists of functions with Lipschitz constant not exceeding m, and the second class consists of functions whose modulus of continuity has a prescribed majorant w. The function w need not be a modulus of continuity.The relative Lipschitz constant of a function h: X ~ R at a point x is defined by I } k(h,x) = sup ~:z) zeX, z#x