The properties of Ceipheids in the Galaxy, LMC, and SMC are analyzed to compare them with theoretical models. The PLC relationships of the LMC and SMC agree with theoretically derived PLC relationships when fitting of data is done by the maximum likelihood method. Differences in the two relationships can be ascribed to abundance differences. Empirical blue edges in the period-color plane agree with models for log P 1.1. Groups (ii) and (iii) have amplitudes in B-V, V, M/sub bol/ and radial velocity that decrease with color. Amplitudes of stars in the Magellanic Clouds do not always follow these same trends, implying systematic differences in amplitude behavior from one galaxy to another.