We present a class of stochastic regime-switching models.
The time-series models may have periodic transition probabilities and
the drifts may be seasonal. In the latter case, the model exhibits
seasonal dummy variation that may change with the regime. The
processes entail nontrivial interactions between so-called business
and seasonal cycles. We discuss the stochastic properties as well as
their relationship with periodic ARMA processes. Estimation and
testing are also discussed in detail.