The chapter presents a view of the oscillation of Czech-Slovak language contact forms in relation to historical, social and political changes as well as the changing conceptualizations of mutual Czech-Slovak language relationships and language ideology affecting the position of contact phenomena in the standard languages. While contact-induced phenomena are more distinct on the lexical level (often opposed by delimitative institutional language management), on the morphosyntactic level language contact leads to less apparent processes, sometimes merely supporting the internal processes of a particular language.