This thesis investigates the patterning of the Algonquian “central agreement”, i.e. the primary person-number agreement marking, from a diachronic and comparative perspective. The central agreement patterns differ in the two orders: in the conjunct it is fusional and often portmanteau while in the independent it is discontinuous and non-portmanteau. In addition to these differences, there are also some commonalities, such as a pattern in which 1p consistently outranks 2p in both orders. This thesis shows that the differences between the two orders can be taken to reflect variation in the features of the syntactic probe and different morphological spell-out rules, while the shared properties follow from the underlying structure of φ-features. In particular, it is proposed that an additional person feature under the [plural] node causes first person plural to be privileged over second person plural in the competition among vocabulary items in post-syntactic spellout.