The main goal of this work is to evaluate the individual and contextual causes that would explain non-compliance by taxpayers via non-declaration. Two different theoretical frameworks have been implemented. Rational choice theories and strain theories. Data stem from a national CIS survey about public opinion and fiscal policy. The sample is representative of adult people residents in Spain (n = 2,464). A series of contingency tables and Multilevel Regression Models report that adverse economic conditions and a low educational-level achievement explain tax fraud. The effects of social class are discussed. The results found that strain theories are more promising than rational choice theories explaining this kind of tax fraud.