Krok po kroku, krok za krokiem, krok w krok - konstrukcje składniowe czy jednostki języka?

The article presents a syntactic and semantic analysis of the expressions krok po kroku 'step by step; one step at a time', krok za krokiem 'step by step; little by little', and krok w krok 'step in step', which are described in the dictionaries as idioms. The analysis confirms the existence of the lexical units of Polish language krok po kroku, krok za krokiem and krok w krok but it also shows that in some contexts these expressions are the result of iterative operations.