There is growing recognition that amino acid availability has profound effects on many aspects of cell function, including the control of membrane transport mechanisms, cell signalling, and gene expression. The precise mechanisms by which amino acids are able to elicit control over such diverse processes have become the focus of intense investigation recently. One particular area that has seen considerable advances is the molecular characterization of amino acid transporters, including members of the System A family, which are known to be regulated by amino acid supply. Recent developments concerning how cells sense and signal amino acid availability, and how this process influences the expression and function of amino acid transporters, are reviewed here. Elucidating the molecular mechanisms of these events will be important in clarifying how amino acid transporters might be regulated during altered nutritional states, and will be crucial for the design of new strategies aimed at improving nutritional support.