Riboswitches are RNA elements that undergo a shift in structure in response to binding of a regulatory molecule. These elements are encoded within the transcript they regulate, and act in cis to control expression of the coding sequence(s) within that transcript; their function is therefore distinct from that of small regulatory RNAs (sRNAs) that act in trans to regulate the activity of other RNA transcripts. Riboswitch RNAs control a broad range of genes in bacterial species, including those involved in metabolism or uptake of amino acids, cofactors, nucleotides, and metal ions. Regulation occurs as a consequence of direct binding of an effector molecule, or through sensing of a physical parameter such as temperature. Here we review the global role of riboswitch RNAs in bacterial cell metabolism.