Robert A. Heinlein
in order.

There's no required order — nearly everything stands alone. A common path is to start with The Moon Is a Harsh Mistress, Starship Troopers, or Double Star, then Stranger in a Strange Land, then explore the juveniles and Future History collections. Only the late 'World as Myth' novels (The Number of the Beast, The Cat Who Walks Through Walls, To Sail Beyond the Sunset) assume knowledge of earlier books.

They're twelve young-adult science fiction novels Heinlein wrote for Scribner's, one a year from Rocket Ship Galileo (1947) to Have Space Suit—Will Travel (1958). Despite the label, they're rigorous, unpatronizing novels that many adults consider some of his best work — Citizen of the Galaxy and Tunnel in the Sky in particular. Starship Troopers was written as the thirteenth but rejected by Scribner's and published as an adult novel.

Very. Heinlein's 1959 novel is a largely earnest exploration of duty, citizenship, and military service with powered armor and relatively little combat, while Paul Verhoeven's 1997 film is a deliberate satire of militarism that mocks many ideas the book takes seriously. Fans of either are often startled by the other.

It's a shared timeline of stories and novels charting humanity's future from the late 20th century through interstellar expansion, sketched on a famous chart Heinlein kept from 1939 onward. The core stories are collected in The Past Through Tomorrow, and the thread continues through Methuselah's Children and Time Enough for Love via the long-lived Lazarus Long.