Cover art
Pratchett, Terry, and Stephen Baxter. The Long Earth. Garper 2012.

Pratchett, Terry, and Stephen Baxter. The Long Earth
Series note: Series including The Long Earth, The Long War, The Long Mars, the Long Utopia, and The Long Cosmos.
Comments: In the 2010s, a device is discovered that allows anyone to step between alternative Earths. The series is, in a sense, not really alternate history, as there is essentially no historical divergence between the parallel Earths and ours. "Datum Earth", in fact, is apparently the only one populated by Homo sapiens.

Pratchett, Terry, and Stephen Baxter. The Long Earth
Summary: In 2015, plans for a device which allows anyone to step from this Earth to parallel Earths are circulated on the Internet and almost everyone starts 'stepping' sideways.
Series note: First volume of The Long Earth series.
Published: Harper 2012 (0062067753BUY), 2013 (0062068687BUY); Doubleday UK 2012 (0857520091), 2013 (0857520105BUY); Corgi 2013 (0552164089BUY).

Pratchett, Terry, and Stephen Baxter. The Long War
Series note: Second volume of The Long Earth.
Published: Harper 2013 (006206777XBUY), 2014 (0062068695BUY), Doubleday UK 2013 (0857520113BUY).

Pratchett, Terry, and Stephen Baxter. The Long Mars
Series note: Third volume of The Long Earth.
Published: Doubleday UK 2014 (0857521748BUY), Harper 2014 (0062326724BUY).