The early days of quantum mechanics were characterised by debates over the applicability of established classical concepts, such as position and momentum, to the new formulation of mechanics. The issues became quite distinct in the protracted exchange between A. Einstein and N. Bohr, culminating in the paper of Einstein, Podolsky and Rosen (EPR) in 1935 (Einstein et al. in Phys. Rev. 47:777, 1935, [1]). Thus the matter rested until 1964 when J.S. Bell (Physics 1:105, 1964; Rev. Mod. Phys. 38:447, 1966, [4]) opened up the possibility of directly testing the consequences of the EPR premises. We will discuss the EPR argument and the analysis of Bell in the context of correlated photon states.