HIV Resistance Response Database Initiative (RDI) is a not-for-profit organisation established in 2002 which states its mission as "To improve the clinical management of HIV infection by developing a large clinical database and bioinformatic techniques that predict accurately any individual's response to any combination of HIV drugs." The RDI states the following specific goals: To be an independent repository of HIV resistance and treatment outcome data To use bioinformatics to explore the relationships between resistance, other clinical and laboratory factors and HIV treatment outcome To develop and make freely available a system to predict treatment response, as an aid to optimising and individualising the clinical management of HIV infection The RDI consists of a small executive group based in the UK, an international advisory group of leading HIV/AIDS scientists and clinicians, and an extensive global network of collaborators and data contributors. Background Human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS), a condition in which the immune system begins to fail, leading to life-threatening opportunistic infections. There are approximately 25 HIV antiretroviral drugs that have been approved for the treatment of HIV infection, from six different classes, based on the point in the HIV life-cycle at which they act. They are used in combination; typically 3 or more drugs from 2 or more different classes, a form of therapy known as highly active antiretroviral therapy or HAART. The aim of therapy is to suppress the virus to very low, ideally undetectable, levels in the blood. This prevents the virus from depleting the immune cells that it preferentially attacks (CD4 cells) and prevents or delays illness and death. Despite the expanding availability of these drugs and the impact of their use, treatments continue to fail, often involving to the development of resistance. During drug therapy, low-level virus replication still occurs, particularly when a patient misses a dose. HIV makes errors in copying its genetic material and, if a mutation makes the virus resistant to one or more of the drugs, it may begin to replicate more successfully in the presence of that drug and undermine the effect of the treatment. If this happens, the treatment needs to be changed to re-establish control over the virus. In well-resourced healthcare settings, when treatment fails, a resistance test may be run to predict which drugs the patient's virus is resistant to. The type of test in most common use is