Evaluation of the steadiness of sprays is possible using the interparticle time distribution-an easily measurable function that contains information about the expected occurrence rate of droplets in a spray. Combined with ensemble-averaging of spray realizations, the interparticle time distribution permits unambiguous classification of sprays on the basis of the time dependence of their intensity function-the probability density for droplet occurrence. Three major spray classifications are defined: steady, unsteady/deterministic, and unsteady/stochostic. Each of the two latter categories may be further refined, leading to the classifications sinusoidal, complex periodic, almost periodic, transient, strictly stationary, N-point stationary, weakly stationary, and nonstationary. Analytical expressions for the interparticle time distribution are derived for each major category of spray using the ideal spray assumptions. Using these expressions, methods are developed that permit unambiguous classification by means of time-series phase Doppler data. The classification methods (and the existence of the classifications themselves) are then demonstrated by application to data from a nominally steady kerosene spray flame.