Strangeness plays an important role in the study of quark matter since it indicates the rate at which new particles are being produced and therefore provides information about the degree of chemical equilibration reached in heavy ion collisions. It is shown that ratios provide an excellent method for determining the temperature and the chemical potential since many theoretical uncertainties cancel out. All indications are that particle abundances are very close to chemical equilibrium. The amount of strangeness present in S−S collisions is very close to the one corresponding to chemical equilibrium. Deviations are at the 30% level.