Filtrations are at the core of some topological data analysis methods. For instance, persistent homology captures the topology of a space by measuring the lifetime of homological events occurring along a given filtration. These kinds of filtration are often induced by considering sub-level sets of continuous functions. A natural question arises about whether any filtration can be generated in this way. In our talk we analyze this problem. In particular, we present a result showing that, under some "natural" conditions, any filtration of a topological space is induced by a continuous function. Both the cases of scalar and vector indexed filtrations are considered.