A framework is presented to model instances of local dependence between items within the context of unidimensional item response theory (IRT). A distinction is made between item main effects and item interactions. Four types of models for interdependent items are considered, on the basis of the distinction between order dependency and combination dependency on the one hand, and dimension-dependent versus constant interaction on the other hand. For each of the 4 model types, variants of the 1-parameter logistic model can be formulated as well as variants of the 2-parameter logistic model. A number of existing IRT models for polytomous items that are variants of the partial credit model may be reconsidered in these terms. Two examples are given to demonstrate the approach.