In vogue with the international currents of public management, the United Kingdom's New Labour government sees the outsourcing, or externalisation, of public service delivery as a key instrument of performance improvement. Evidence suggests, however, that a significant proportion of local authorities are reluctant to externalise. On the basis of fifty interviews in six case-study authorities, the author identifies five reasons for a reluctance to externalise. He further considers the degree of theoretical support for this reluctance, concluding that gaps in our knowledge-critical to 'make or buy' decisions-make it impossible to determine whether a reluctance to externalise is well founded or not.