The objective of this paper is to generalize the concept of fuzzy sets from a real space to a topological space. If the crisp sets are nested and ordered by set inclusion in the reverse way that their subscripts are ordered by the usual ordering in the real line, they can constitute a fuzzy set. Moreover, it is always feasible to construct a fuzzy set which possesses a continuous membership function on a normal space if the crisp set from which a fuzzy set is constructed is a nonempty open set.