See the works of:
<ul>
<li>_(Solomon Feferman | http://math.Stanford.EDU/~feferman/) did a lot of work.
<li>Raymond Smullyan
<li>_(John Harrison's review | http://portal.acm.org/citation.cfm?id=235792&coll=portal&dl=ACM&CFID=11111111&CFTOKEN=2222222)?
<li>_(NuPrl)
<li>_(Jos Meseguer | http://www.cs.uiuc.edu/people/faculty/meseguer.html) headed the _(Rewriting Project | ) at SRI, resulting mainly in _(Maude). See also _(Semantic Foundations for Compositions | http://www.darpa.mil/ito/psum1997/D898-0.html).
<li>_(Samuel Boutin | http://pauillac.inria.fr/~boutin/) wrote a PhD thesis on reflection and quotients in _(Higher-Order Logic)s.
<li>_(R.B. Jones' | http://www.rbjones.com) _(page on logic | http://www.rbjones.com/rbjpub/logic/)
<li> _("Aurlien Slodzian"|http://www-poleia.lip6.fr/~slodzian/) (_("old homepage"|http://arti.vub.ac.be/~as/) _(MIA)) has written a paper on _("knowledge-level reflection"| http://arti.vub.ac.be/~as/papers/kl-reflection/kl-reflection.html) [_(MIA) can be found on _(citeseer|http://citeseer.nj.nec.com/slodzian94knowledge.html)].</li>
<li>Another paper on knowledge-level reflection, _(here|http://citeseer.nj.nec.com/522004.html).</li>
</ul>
