The microtype package includes a tracking option, in which the space between letters is increased. This should normally be done for sequences of both full caps and small caps, see e.g. Bringhurst's style book.
The tracking set by microtype, however, appears only in upright small caps, not for italicized small caps, and not for full caps at all. I find this somewhat odd, and it honestly looks inappropriate in a document that uses all of them. Is there a way to circumvent this problem?
\documentclass{article}
\usepackage[tracking = true]{microtype}
\usepackage{libertine}
\begin{document}
ABCD \textsc{abcd} \textit{ABCD \textsc{abcd}}
\end{document}


fontspecandluatex? – Sverre Jun 07 '14 at 13:58pdftex, only that you need to specify the right encodings (ie. those from the default setsmallcapsfrommicrotype.cfg). [I've edited the answer accordingly.] – Robert Jun 18 '14 at 00:09