Delta IV is an active expendable launch system in the Delta rocket family. Delta IV uses rockets designed by Boeing's Integrated Defense Systems division and built in the United Launch Alliance (ULA) facility in Decatur, Alabama. Final assembly is completed at the launch site by ULA. The rockets were designed to launch payloads into orbit for the United States Air Force Evolved Expendable Launch Vehicle (EELV) program and commercial satellite business. Delta IV rockets are available in five versions: Medium, Medium+ (4,2), Medium+ (5,2), Medium+ (5,4), and Heavy, which are tailored to suit specific payload size and weight ranges. Delta IV was primarily designed to satisfy the needs of the U.S. military.

The rockets are assembled at the Horizontal Integration Facility for launches from SLC-37B at Cape Canaveral, and in a similar facility for launches from SLC-6 at Vandenberg AFB.

The Delta IV entered the space launch market at a period when global capacity was already much higher than demand. Furthermore, as an unproven design it has had difficulty finding a market in commercial launches, and the cost to launch a Delta IV is somewhat higher than that for competing vehicles. In 2003, Boeing pulled the Delta IV from the commercial market, citing low demand and high costs. In 2005, Boeing stated that it may return the Delta IV to commercial service; however as of 2006^[update] no further announcements have been made regarding this. All but one of the first launches have been paid for by the U.S. Government, with a cost of between $140 million and $170 million.

Delta commonly refers to:

Delta may also refer to:

Along with the aforementioned Delta Airlines, other companies named Delta include:

, an inverted delta representing del, a vector differential operator

, the Kronecker delta function

, the Dirac delta function