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We introduce description logic (DL) rules as a new rule-based formalism for knowledge representation in DLs. As a fragment of the Semantic Web Rule Language SWRL, DL rules allow for a tight integration with DL knowledge bases. In contrast to SWRL, however, the combination of DL rules with expressive description logics remains decidable, and we show that the DL [Sscr][Rscr][Oscr][Iscr][Qscr]–the basis for the ongoing standardisation of OWL 2–can completely internalise DL rules. On the other hand, DL rules capture many expressive features of [Sscr][Rscr][Oscr][Iscr][Qscr] that are not available in simpler DLs yet. While reasoning in [Sscr][Rscr][Oscr][Iscr][Qscr] is highly intractable, it turns out that DL rules can be introduced to various lightweight DLs without increasing their worst-case complexity. In particular, DL rules enable us to significantly extend the tractable DLs [Escr][Lscr]++ and DLP.