This paper presents an analysis of constructions involving the l-form of the verb in Polish, including primarily the past tense, the conditional mood, and the future tense. Previous approaches have attempted to treat these uniformly as auxiliary verb constructions. We argue against a unified treatment, however, in light of synchronic and diachronic evidence that indicates that only the future tense and the conditional still involve auxiliaries in modern Polish. We show that the past tense is now a simple tense, although the l-forms appear in combination with agreement affixes that can appear in different places in the sentence. We provide an account of the common linearization properties of the past tense markings and the conditional auxiliary. We present a detailed HPSG analysis of the past tense construction that relies on the introduction of two interacting agreement features. We then discuss the consequences of our proposals for the analysis of the conditional and future auxiliary constructions, and finally, we offer a treatment of constructions involving inflected complementizers in Polish.