From VISTA's strategy document 2014 - 2019:
VISTA supports a professorship at all times. The objective is to "liberate" a researcher of excellent repute so that he or she can work full-time on research and research supervision within their field of expertise. Part-time professorships may be considered in exceptional cases. The professorship is granted on the proviso that there is a research plan for the period of appointment and that the professor will be working at a recognised research institution.
The professorship may be used to recruit internationally leading candidates with a view to building up expertise in an important priority area for VISTA.
The VISTA professorship is normally advertised every three years. Institutions apply for the VISTA professorship themselves, and the applications are processed by the VISTA board.