This is a study of processes of structural and functional diversification of the uses of three cognate verbs across the Indo-Iranian language family: "do/make", "be/become", and "give". First, this study identifies over sixty distinct construction types in which these verbs are used, including complex predicate constructions, nominal predication constructions, serial verb constructions, and several distinct auxiliary constructions. Since the sets of verbs studied here are cognates, and share a common source, crosslinguistic differences in their uses are the result of grammatical change, and especially shared and parallel innovations of similar uses. Then, this study presents a taxonomy of different complex predication types with "do/make", and shows that there are general patterns in the deployment of different types of complex predication to express different types of situations. These patterns exhibit "transitivity prominence" previously identified by typologists with "heavy" or "lexical" verbs. This study then shows that these patterns are the result of several distinct pathways of grammatical change, often motivated by analogy to existing constructions, giving raise to different types of N-V complex predication constructions. Then, this study shows that despite the fact that Indo-Iranian speakers can potentially deploy distinct constructions to encode each of the six nominal predication functions, sets of such functions are often co-expressed by the same structural coding means, especially clauses with cognate "be/become" verbs. This study uses a novel method, based on bipartite network graphs, to compare of the degree to which nominal predication functions are co-expressed in different languages. Finally, this study shows that the three sets of cognate verbs are more likely to be used similarity within branches and subbranches of Indo-Iranian than across branches. The scope of this branches, however, is different for different verbs: "do/make" and "give" behave more similarly in languages which belong to the same major branch, Iranian or Indo-Aryan, but "be/become" clusters are at different levels of subbranching. This is the result of the different types of innovations attested with these verbs: reanalysis and actualization motivated by analogy with "do/make" and "give", and metaphorical and metonymy extensions with "be/become". [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]