In this paper we consider bilevel equilibrium and optimization problems with equilibrium constraints.  We propose are laxed level closedness and use it together with pseudo continuity assumptions to establish suf?cient conditions for well-posedness and unique well-posedness. These conditions are new even for problems in one dimensional spaces, but we try to prove them in general settings. For problems in topological spaces, we use convergence analysis while for problems in metric cases we argue on diameters and Kuratowski?s, Hausdorff?s, or Istrătescu?s measures of noncompactness of approximate solution sets. Besides some new results, we also improve or generalize several recent ones in the literature. Numerous examples are provided to explain that all the assumptions we impose are very relaxed and can not be dropped.