Abstract. The monster tower is a tower of spaces over a specified base; each space in the tower is a parameter space for curvilinear data up to a specified order. We describe and analyze a natural stratification of these spaces.The monster tower, also known in the algebro-geometric literature as the Semple tower, is a tower of smooth spaces (varieties) over a specified smooth base M. Each space M(k) in the tower, called a monster space, is a parameter space for curvilinear data up to order k on M. We will describe a coarse stratification of each monster space, with each stratum corresponding to a code word created out of a certain alphabet according to rules that we will specify. These strata parametrize curvilinear data "of the same type." The monster space can be regarded as an especially nice compactification of the parameter space for curvilinear data of nonsingular curves on M (as explained in Section 2), with the added points representing the data of singular curves; in our stratification the nonsingular data points will form a single open dense stratum.Versions of this coarse stratification have been observed by virtually everyone who has studied the monster construction. Here we develop the theory in full generality, beginning with a base space of arbitrary dimension and at all levels. A finer stratification would result from a thorough analysis of the orbits under the action of a suitable group acting on the base (whose action can be lifted to the tower) or, working locally, of the pseudogroup of local diffeomorphisms at a selected point. Results such as those in Section 5.7 of [12] show that one can expect there to be infinitely many strata, i.e., that there are moduli. We seem to be very far, however, from a full understanding of where and why moduli occur.