  This article describes blavaan, an R package for estimating Bayesian
structural equation models (SEMs) via JAGS and for summarizing the results. It
also describes a novel parameter expansion approach for estimating specific
types of models with residual covariances, which facilitates estimation of
these models in JAGS. The methodology and software are intended to provide
users with a general means of estimating Bayesian SEMs, both classical and
novel, in a straightforward fashion. Users can estimate Bayesian versions of
classical SEMs with lavaan syntax, they can obtain state-of-the-art Bayesian
fit measures associated with the models, and they can export JAGS code to
modify the SEMs as desired. These features and more are illustrated by example,
and the parameter expansion approach is explained in detail.
