Packer permeability tests are used routinely in geotechnical investigations to allow estimation of hydraulic conductivity by analysis of pressure/flow rate response during controlled injection of water into a section of borehole, isolated by packers. This paper is a review of the hydraulic fundamentals of the packer permeability test methods and analyses used routinely in geotechnical investigations and discusses the usefulness and limitations of the test. Guidance is given on design of tests, including the maximum hydraulic conductivity that can be measured by the method. Interpretation of tests must recognise that responses are influenced by the entire test system – the host rock, the borehole and any associated zone of disturbance, water quality (injected water and water in the host rock), packers or isolation system and the head/flow rate measurement system. It is proposed that, for geotechnical projects, presenting test results as a Q-H diagram (plotting injection flow rate vs. applied excess head) is useful and allows results to be classified against seven conventional and three unconventional test responses (which expand on earlier work by Houlsby (1976) and others). Guidance is given on the selection of values of hydraulic conductivity, for geotechnical design purposes, from various types of test responses.