This chapter presents the fundamental theoretical principles underlying our research. It starts with the theoretical foundations of examining word-formation creativity, in particular, the system of onomasiological types, and the conception of the competition between two contradictory tendencies that can be identified (not only) in the field of word-formation, namely, semantic transparency and economy of expression. This is reflected in two scales of semantic transparency and economy of expression, including their underlying principles. The principle of Creativity within and beyond Productivity Constraints is justified. This is followed by presenting the theoretical foundations underlying our research into interpretation creativity, that is, a theory of meaning predictability reflected in an integrated onomasiological model of complex words. Attention is paid to the parameters used for the evaluation of interpretation creativity. They include Predictability Rate, Objectified Predictability Rate, the average number of readings proposed by a cohort member, and hapax legomena.