Universal Century

• Mobile Suit Gundam: The Origin (OVA, 2015)
• Mobile Suit Gundam (TV Series, 1979)
• Mobile Suit Gundam: The 08th MS Team (OVA, 1995)
• Mobile Suit Gundam 0080: War in the Pocket (OVA, 1989)
• Mobile Suit Gundam Thunderbolt (ONA, 2015)
• Mobile Suit Gundam 0083: Stardust Memory (OVA, 1991)
• Mobile Suit Zeta Gundam (TV Series, 1985)
• Mobile Suit Gundam ZZ (TV Series, 1986)
• Mobile Suit Gundam: Char's Counterattack (Movie, 1988)
• Mobile Suit Gundam Unicorn (OVA, 2010)
• Mobile Suit Gundam: Twilight AXIS (ONA, 2017)
• Mobile Suit Gundam Narrative (Movie, 2018)
• Mobile Suit Gundam F91 (Movie, 1991)
• Mobile Suit Victory Gundam (TV Series, 1993)

Future Century

• Mobile Fighter G Gundam (TV Series, 1994)

After Colony

• Mobile Suit Gundam Wing (TV Series, 1995)
• Mobile Suit Gundam Wing: Endless Waltz (OVA, 1998)

After War

• After War Gundam X (TV Series, 1996)

Correct Century

• Turn A Gundam (TV Series, 1999)

Cosmic Era

• Mobile Suit Gundam SEED (TV Series, 2002)
• Mobile Suit Gundam SEED Destiny (TV Series, 2005)

Anno Domini

• Mobile Suit Gundam 00 (TV Series, 2007)
• Mobile Suit Gundam 00: A wakening of the Trailblazer (Movie, 2010)

Advanced Generation

• Mobile Suit Gundam AGE (TV Series, 2011)
• Mobile Suit Gundam AGE: Memory of Eden (OVA, 2013)

Regild Century

• Gundam Reconguista in G (TV Series, 2014)

Post Disaster

• Mobile Suit Gundam: Iron-Blooded Orphans (TV Series, 2015)

Gunpla Battle series

• Gundam Build Fighters (TV Series, 2013)
• Gundam Build Fighters: GM's Counterattack (OVA, 2017)
• Gundam Build Fighters Try (TV Series, 2014)
• Gundam Build Fighters Battlogue (OVA, 2017)
• Gundam Build Divers (TV Series, 2018)
• Gundam Build Divers Re:RISE (OVA, 2019)

NOTES

• The original Mobile Suit Gundam TV series has weak pacing. I recommend watching the compilation movie trilogy instead.
• Gundam F91 and Victory Gundam are set 30 and 60 years after Char's Counterattack, respectively. They're not connected to any other conflicts in the timeline and are thus not necessary toward understanding the overarcing plot of the rest of the timeline.
• To get the most out of Turn A Gundam and Reconguista in G, don't watch them until after watching the big four Universal Century installments (Gundam 1979, Zeta Gundam, Gundam ZZ, Char's Counterattack).