The last several years have seen an explosion of activity in the field of critical phenomena in general. This enormous interest in the thermodynamic singulari­ ties and long range spatial correlations existing at a second order transition was triggered by the realization that the Landau universal phenomenological theory of critical phenomena ( l ) is incorrect for most real systems. That it was incorrect for at least one nontrivial model (the two-dimensional Ising model) had been known for many years, but the real moment of truth came with increasing experimental precision showing "nonclassical" behavior in a rapidly growing number of actual experimental systems as the critical temperature Tc is ap­ proached. Theoretical insight began with the development of series expansions for simple model systems (2) and the examination of extrapolation techniques for estimat­ ing limiting behavior of a power series from a knowledge of only its first several terms. The findings can sometimes be subjective and unconsciously swayed by the climate of opinion of the moment. In spite of this there were very strong indications that sufficiently close to a critical point most physical quantities varied as simple power laws (3) but with nonclassical critical exponents often approximating those inferred from experiment (4). Nothing can be proved, unfortunately, by series extrapolation, and there remains a dearth of rigorous theorems concerning critical phenomena. Some proofs (leading to exponent inequalities) have been obtained with considerable rigor from basic thermodynamics and statistical mechanics; however, series extrapolation methods remain the most reliable tool for the theoretical investiga­ tion of critical exponents.