Vespa Haynes Owners Workshop Manual 1959-1978:

This book is an old faithful repair book published in 1990. It notes that it covers all Vespa models from 1959 to 1978 but in reality it covers the Vespa 90 (V9A1T), 90 SS(V9SS1T), Racer (V9SS2T), Douglas 232L2, 125 (VMA1T), Primavera (VMA2T), Vespa 150/Douglas Sportique (VBB1T), 150 Super (VBC1T), GL150 (VLA1T), Sprint 150 (VLB1T), Rally 180 (VSD1T), and Rally 200 (VSE1T). It doesn't cover the GS150 (VS51T) which was built until 1961. These models covered are similar enough to most others that the principles are the same even if the bike you have is not covered in the list above. The book has photographs of a complete dismantling of a VBB style bike, and expands to small frames with only a few exploded views. It has many helpful troubleshooting guides and general maintenance that is required at periodic intervals.

Vespa Haynes Owners Workshop Manual 1978 - 1988:

This is the book for all P-Series bikes up to 1988 and covers most P-series bikes up to today in terms of mechanics although the electric pages will not be current and other more recent features like electric start are not covered as it was published in 1985. Both books cover the Vespa P125X (VNX1T), PX125E (VNX2T), T5 (VNX5T), P150X & PX150E (VLX1T), P200E & PX200E (VSX1T). The book on the left also covers the T5 with a supplement section at the rear of the book covering the gearbox differences, specifications, and headlight assembly.

The First Book of Vespa by J. Emmet:

Thanks to Dylan Aster I found that it was also published as the Vespa Scooter Owner's Manual in the USA (the two books are exactly the same inside). This is the earliest book I have found in the Pitman Motor Cycle Library that deals with Vespa scooters. It covers all the widemount engined Vespa 125s and 150s starting with the Vespa 125 (VM1T) from 1951 to the last widemount, the GS150 (VS51T) which was last produced in 1961. It also covers the Douglas 42L2 and Clubman in the last few pages of the book. It has more text than diagrams but is helpful and could allow a resourceful owner to do a major renovation or engine work. Lastly, it covers general maintenance and adjustments.

Vespa - A Practical Guide by R.V. Bryant

This book covers Douglas models (Vespas built under license in England), It covers all the widemount engined Douglas Vespas starting with the Rod model in which was the first model produced in 1951. It also covers the G model, the GL2, 42L2, 92L2, Continental, 102L2, Clubman, 152L2, 312L2 Sportique, and the 232L2. This book doesn't stop at the Douglas models and continues on to the Vespa GS150 (VS1T through VS5T), 150 (VBA1T), GS160 (both series), 90 (V9A1T), and finishes up with the Messerschmitt GS150 made under license in Germany and the ACMA Vespa made in France (same as 92L2).

It starts with an excellent overview of how a two stroke works, explaining transfers, rotary valves, transmission, lubrication, etc.. Basic maintenance is then covered before diving into a major technical breakdown of each bike with very good technical diagrams, electrical diagrams, and a fantastic fault finding chart.

Votre Vespa - by Editions Pratique Automobiles

This book covers Vespa widemount models from 1951 to 1954. It is from France so obviously all the text is in French..

It has many pictures of a full engine disassembly with all the fancy purpose built tools of the day, two page pull out diagrams of parts and exploded drawings, and full specification and wear tolerances for major parts. Front and back cover insides have old french adds for helmets, and piston rings. Handy if you speak French but very useful regardless.