Harry Harrison’s The Deathworld Trilogy consists of three works: 1960’s Deathworld, 1964’s Deathworld 2, and 1968’s Deathworld 3. Alternate titles: Deathworld, The Ethical Engineer, and The Horse Barbarians. All were serialized in the same magazine, which was known as Astounding when Deathworld was published and Analog when the other two came out.
(The Deathworld series is much longer. More on that later.)