The article aims to present and discuss five theoretical models explaining the issue of ideological changes in Polish political parties. The paper is to shed light on an ideology’s dynamic nature and the process of building ideology in the political parties’ environment. The article features a discussion on the circumstances favoring the implementation of ideological changes and the methods used by parties to implement changes in their ideologies. The paper adopts two research hypotheses: 1) party ideologies are developed and modified by political parties in response to the changing (social, political, economic) circumstances in the inter-party rivalry. 2) The process of ideological changes serves political parties to lead an effective inter-party rivalry. The paper establishes that the factors with scientifically documented impact on party behavior in ideological terms are as follows: electoral result (parties that achieved a result below their expectations are more eager to revise their ideologies), political competition’s activity (parties react to ideological changes of their direct rivals), electorate preferences (political forces can change their approach in crucial issues to reflect the dominant views in their electorates) and acceptance of free-market principles by the main political actors. An analysis of Polish parties’ behaviors and the gathered source material also demonstrates that the parties’ inclination to implement ideological changes depends on organizational factors.