Daystar or day star may refer to:

• Day Star, 1878 Kentucky Derby winner
• DayStar Digital, a company that used to manufacture Apple Macintosh clones
• Daystar Technologies, a company that builds performance upgrades for Apple Macintosh Computers and services the previous company's products
• Daystar (TV network), an evangelical Christian satellite network
• Daystar University, a Christian liberal arts college located in Kenya
• Lucifer, a name that in English generally refers to the Devil or Satan
• Venus, as it appears on the morning or evening horizon
• The Sun
• Daystar, a character in Patricia C. Wrede's Enchanted Forest Chronicles
• Daystar, a virus created to kill vampires in the movie
• Daystar Productions, the production company founded by Leslie Stevens that produced the 1960s TV series The Outer Limits and the earlier series Stoney Burke and a few films
• Daystar, a 2002 album by shoegazing band Lab Partners.

DayStar Technologies, Inc. is a publicly traded solar energy company located in Santa Clara, California. Its primary product is a thin film photovoltaic material on a glass or plastic substrate. These thin film solar modules are manufactured using copper indium gallium (di)selenide (CIGS), which has shown a 19.5% NREL efficiency in real world conditions, slightly above CdTe and significantly above amorphous silicon. As part of their initiative to become a more integrated global renewable energy company, Daystar undertook to purchase Eco Energy Solutions Australia Pty Ltd on June 4, 2012 with a binding letter of intent. Daystar failed to consummate the transaction by tendering cash and shares as per this agreement. As a result, the Managing Director of Eco Energy Solutions and Daystar Technologies board member were forced to place Eco Energy Solutions into liquidation. This resulted in the lodgement of a lawsuit in the United States to recover losses from Daystar Technologies International.