The Milestone Universe began as an independent imprint published by DC.
At that point, it was set in its own separate universe. Later, it crossed over with the DC Universe, and later still, it was merged into the DC Universe proper. This timeline largely ignores these universal transitions in favour of listing character appearances in a more or less chronological order.
The Milestone Universe
Icon: A Hero’s Welcome- Reprints Icon #1-8 (May – December 1993)
- Hardware: The Man in the Machine
- Reprints Hardware #1-8 (April – October 1993)
- Static Shock: Trial by Fire
- Reprints Static #1-4 (June – September 1993)
- Icon: The Mothership Connection
- Reprints Icon #13, 19-22, 24-27, & 30 (May 1994, December 1994 – February 1995, April – July 1995, October 1995)
- Static Shock: Rebirth of the Cool
- Reprints Static #1-4 (June – September 1993) and Static Shock!: Rebirth of the Cool #1-4 (January 2001 – September 2001)
The DC Universe (post-Final Crisis)
After the events of Final Crisis
- The Brave and the Bold: Milestone
- Reprints The Brave and the Bold #24-26 (August – October 2009), Static #12 (May 1994), Hardware #16 (June 1994), and Xombi #6 (November 1994).
Features Static (teaming up with Black Lightning), Hardware (teaming up with Blue Beetle) and Xombi (teaming up with the Spectre). 
Terror Titans- Reprints Terror Titans #1-6 (December 2008 – May 2009)
Features Static. - Justice League of America: When Worlds Collide
- Reprints Justice League of America #27, 28 & 30-34 (January, February, April – August 2009)
Features Hardware, Icon, Rocket and the Shadow Cabinet. Hardware specifically states that this story occurs after his team up with Blue Beetle. - Teen Titans: Changing of the Guard
- Reprints Teen Titans vol. 3, #62–69 (October 2008 – May 2009)
Features Static. - Teen Titans: Deathtrap
- Reprints Teen Titans vol. 3, #70 (June 2009), Annual 2009; Titans vol. 2, #12–13 (June – July 2009) and Vigilante #5-6 (June – July 2009).
Features Static. - Teen Titans: Child’s Play
- Reprints Teen Titans vol. 3, #71–78 (July 2009 – February 2010)
Features Static. - Superman: Mon-El
- Reprints Action Comics #874 (April 2009) and a Mon-El from Annual #10 (March 2007); Superman #684-690 (March – September 2009); and material from Superman: Secret Files 2009 #1
Features Icon, Static and Iron Butterfly in cameos (they are seen on monitors, being watched by a paranoid government agency). - Teen Titans: The Hunt for Raven
- Reprints Teen Titans vol. 3, #79–87 (March – November 2010).
Features Static. - Xombi
- Reprints Xombi (vol. 2) #1-6 (May 2011 – October 2011)
The New 52 Universe (post-Flashpoint)
It is still unclear how much most Milestone characters have been affected by Flashpoint and the New 52 reboot. However, given that Static and Hardware are both currently appearing in the revived Static Shock title, their story is clearly not over yet.
- Flashpoint
- Reprints Flashpoint #1-5 (July 2011 – Late October 2011).
At the conclusion of the story, Static appears, presaging his new series. - Static Shock, vol.1: Supercharged
- Reprints Static Shock #1-8 (November 2011 – June 2012)
Hardware also appears in this book. - The Savage Hawkman, vol.1: Darkness Rising
- Reprints The Savage Hawkman #1-8 (November 2011 – June 2012)
Static teams up with Hawkman in issue #7.
