From the publishers website:
"Retro, 5th edition is a tactical, squad-level World War II combat variant rules set contained in a 56-page book. Its goal is to provide players--experienced and inexperienced alike--with simplified rules to enable them to play and enjoy tactical wargames and modules without having to master hundreds of pages of rules and a steep learning curve. You must own the necessary components (counters and mapsheets) of the "host" game to utilize Retro.
Retro, 5th edition consists of a 56-page rulebook, containing all standard, advanced, and optional rules, eleven scenarios, two double-sided Reference cards, and instructions for creating design-your-own scenarios. The standard rules from the 36-page 4th edition (2012) are unchanged, apart from some verbal smoothing and explication. The 5th edition adds twenty pages, and includes more optional rules and scenarios. New rules cover FIRE (starting and spreading), MINEFIELDS, a new HESITATION OPTION, PARATROOP DROPS, NATIONAL TROOP CHARACTERISTICS, CAPTURED ENEMY SW, new designer notes, and more. It has been published in soft cover book format, with color Reference Cards, and looks sharp. Retro fans will be pleased with what the new edition provides!"