Welcome to the world of OUTLANDER books. There are 8 books altogether in the series.
OUTLANDER is book number one.
Book 2 is DRAGONFLY IN AMBER
Book 3 is VOYAGER
DRUMS OF AUTUMN is Book 4
Book 5 is THE FIERY CROSS
Book 6 is A BREATH OF SNOW AND ASHES
ECHO IN THE BONE is Book 7
Book 8 is WRITTEN IN MY OWN HEART'S BLOOD