Retrograde Planets by Grace Inglis

One of the finest book on retrogression of planets under guidance of Manik Chand Jain including lots of original research

Retrograde Planets: Traversing the Inner Landscape by Erin Sullivan

Hindu Dasa System by Grace Inglis

Vakri Planets (Retrograde Planets) by M Subba Rao

Burn Rates: Retrogrades in Astrology – Retrograde Planets by Michael Erlewine

Karmic Astrology: (Volume II) Retrograde Planets and Reincarnation by Martin Schulman

Mystery Of Retrograde Planets by M G Kastwar

Retrograde Planets by Raj Kumar

Retrograde Planets (Part 1 -Jupiter and Venus) by Himanshu Shangari