Methusaleh's Children featured an experimental FTL drive by one of the characters that was essential to the plot; in Time Enough for Love , its sequel the same FTL drive is discovered to also work as a time-travel drive.
The Number of the Beast , The Cat Who Walks Through Walls , and
To Sail Beyond the Sunset all have a universe-hopping device that serves as an FTL stand-in Starship Troopers
involves FTL, as Michael indicated, the book doesn't really get into details.
Tunnel in the Sky
and, I think, Have Spacesuit - Will Travel and Starman Jones all involve FTL or similar systems, at least peripherally.
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From the Faster Than Light and Normal Space Starship and Spaceship Drive List ... Number of the Beast .
Based in a 6-dimensional space, you can instantaneously travel to where you want to go provided you know the proper vectors.
Starman Jones .
The starship in question accelerated to the speed of light where itjumped elsewhere.
The Cat Who Walks Through Walls ,
To Sail Beyond The Sunset .
Drive is size of a sewing machine case and can instantaneously place the vessel anywhere, anywhen, in any universe with a velocity up to the speed of light.
Computer controlled and uses virtually no power.
Future History .
In one of the Lazarus Long stories an inertialess drive is used to go FTL.
Possibly Starship Troopers and Citizen of the Galaxy ...
but I don't remember the references.
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In addition to those already mentioned: Friday Citizen of the Galaxy
The Star Beast
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I believe Starship Troopers had FTL, but I am unclear as to how it works.
The book dealt more with planetary assaults than with space travel.
They were definately on other planets, though.
Another book of his had "gates" to other planets, through which colonization expeditions proceeded.
I do not recall the title - please edit or leave a comment if you know it.
It was Tunnel in the sky .
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I think Time for the Stars is the only one no-one else has mentioned.
After they've spent most of the book travelling relativistically, an FTL drive is introduced at the end of the book.
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I'm a new Heinlein fan and also an FTL (faster-than-light) fan.  Did he write any books where FTL was possible?  All the ones I've read so far have been intra-system (Sol) only.
Heinlein book(s) with FTL travel?
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<robert-a-heinlein><ftl-drive>
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Methusaleh's Children featured an experimental FTL drive by one of the characters that was essential to the plot. In  Time Enough for Love, the same FTL drive is discovered to also work as a time-travel drive. Number of the Beast, Starman Jones, To Sail Beyond The Sunset and Future History, as well as possibly  Starship Troopers and  Citizen of Galaxy all featured FTL. Methusaleh’s Children, Number of the Beast, Starman Jones, To Sail Beyond the Sunset, Future History, Starship Troopers, Citizen of the Galaxy and Time for the Stars.
Methusaleh’s Children, Number of the Beast, Starman Jones, To Sail Beyond the Sunset, Future History, Starship Troopers, Citizen of the Galaxy and Time for the Stars.