This paper studies some grammaticalisation phenomena in the verb system in Iranian. It will specifically look at those categories where grammaticalisation features prominently: while not all categories of the verb system show grammaticalisation processes, some do so in a large number of Iranian languages, and using the same morphological elements. Transitivity is a category of high grammaticalisation activity in Iranian. It is marked by analogical extension of inherited verbal stem formation as well as by the introduction of a number of double paradigms in the PAST domain (which arise as the inherited aorist and perfect stems are lost in late Old Iranian): the “inchoative suffix” -s- is used for the formation of secondary intransitives in several Middle Iranian languages, and new suffixes arise for the formation of causatives. While the intransitive perfect / past is expressed by the perfect participle / past stem with the copula in most of Middle Iranian and later on, the transitive paradigm shows a different pattern: Khotanese employs an enlarged form of the perfect participle, some languages form ergative constructions and others use a transitive auxiliary. As is common for auxiliaries in grammaticalisation processes, phonological reduction occurs; so the verb ‘hold/have’ that forms the transitive perfect in Sogdian (in a pattern entirely parallel to Germanic and Romance have vs. be perfects) merges with the past stem, and the origin of the transititive formation in Ossetic is not transparent any more (probably Ir. *dā- < PIE *dheh1 ‘put’, thus parallel to Latin formations of the type rube-facio ‘make red’). Secondly, the categories of particularly high grammaticalisation activity themselves appear to form clusters. A small number of verbs are used as auxiliaries in various patterns: ‘do’, ‘hold’ and ‘put’ on the transitive / active side and ‘be’ as well as verbs of movement on the intransitive / passive side (perfect / past domain, passive voice, intransitive / passive pairs of the potential construction). The same verbs are also the most prominent light verbs, suggesting that the rise of complex predicates is a process parallel to the grammaticalisation of auxiliaries. Both periphrastic verbal patterns and complex predicates come in pairs of a transitive / active and a intransitive / passive counterpart; it thus seems that categories of transitivity, control and actionality forms one cluster of particularly high grammaticalisational activity in Iranian. Another cluster is the field of aspect, durativity and mood. Progressives (often becoming present tense formations) may be grammaticalised by particles or locational constructions (‘I am [in the position of] going’). Auxiliaries are also found, among which, again, is ‘hold/have’ and the verb ‘stand’, recalling the use of verbs of movement in intransitive / patterns just mentioned. A third field of particular interest is animacy and person marking. Differential marking of direct and indirect objects as well as of agents in the ergative domain is common throughout Iranian and is expressed by case suffixes and adpositions. A possibly related phenomenon is the conversion of demonstratives to copula forms, by which process gendered copula forms of the 3SG arise in languages as diverse as Pashto and Zazaki. Conversely, verbal endings assume pronominal function following a loss of case distinctions and changes in ergativity patterns.