  The individuality of head-related transfer functions (HRTFs) is a key issue
for binaural synthesis. While, over the years, a lot of work has been
accomplished to propose end-user-friendly solutions to HRTF personalization, it
remains a challenge. In this article we establish a state-of-the-art of that
work. We classify the various proposed methods, review their respective
advantages and disadvantages, and, above all, methodically check if and how the
perceptual validity of the resulting HRTFs was assessed.
