Ernie Lepore and Jerry Fodor have published a series of original and controversial essays on issues relating to compositionality in language and mind; they have now revised them all for publication together in this volume. Compositionality is the following aspect of a system of representation: the complex symbols in the system inherit their syntactic and semantic properties from the primitive symbols of the system. Fodor and Lepore argue that compositionality determines what view we must take of the nature of concepts. Anyone trying to figure out how language and mind work must take account of this challenging work by two leading figures in the field.