This chapter considers, with particular reference to the evaluation work of the UK Overseas Development Administration (ODA), how evaluation of technical co-operation (TC) expenditures is done and whether anything could be done to make our knowledge of the impact of TC programmes more exact. TC – aid embodied in human beings – has often been praised as a particularly cost-effective means of accelerating development in poor countries and has accounted for an average of about one-fifth of the total aid disbursement. The output of a TC project is the increase in knowledge made possible by the expenditure of aid money, together with its impact on the recipient economy. The onus of obtaining value for money in TC lies entirely with the donor. ODA evaluation reports, in a majority of cases, confine themselves to measuring input into TC projects, when they need also to be measuring output.