Toaru Kagaku no Accelerator: Tobidase Ippou-san - Hachamecha Kaishingeki

My interpretation of the Toaru Series Watch Order.

A comprehensive watch order of the Toaru Series series, which includes every entry of the Toaru Series franchise.
Original Guide: https://myanimelist.net/forum/?topicid=1867550

Release Order

Follow the items list order.

Chronological Order

According to the Index wiki, the chronological order for the series is as followed:
(version with links in the original guide thread comments)

Level Upper Arc
Railgun episodes 1-14.
Railgun OVA episode 1.

Index Arc
Index episodes 1-6.

Big Spider Arc
Railgun episodes 15-16.

Deep Blood Arc
Index episodes 7-9.

Poltergeist Arc
Railgun episodes 17-24.

Sisters Arc
Railgun S episodes 1-9.
Index episodes 10-14.
Railgun S episodes 10-16.

Silent Party Arc and Angel Fall Arc
Railgun S episodes 17-20.
Index episodes 15-17.
Railgun S episodes 21-24.

Three Stories Arc
Index episode 18.
Index II episode 1.
Index episodes 19-20.

Kazakiri Hyouka Arc
Index episodes 21-24.

Necromancer Arc
Accelerator episodes 1-12.

Orsola Aquinas Rescue Arc
Index II episodes 2-5.

Toaru Majutsu to Kagaku no Ensemble
Visual Novel for the PSP (optional).

Tree Diagram Remnant Arc
Index II episodes 6-7.

Toaru Majutsu no Index Movie
Index Movie: Endymion no Kiseki

Daihasei Festival Arc
Railgun T episodes 1-3.
Index II episodes 8-13.
Railgun T episodes 4-15.

La Regina del Mare Adriatico Arc
Index II episodes 14-16.

Dream Ranker Arc (Introduction)
Railgun T episodes 16-17, 19.

Academy City Invasion Arc
Index II episodes 17-23.

Skill-Out Uprising
Index II episodes 23-24.

Dream Ranker Arc (Indian Poker)
Railgun T episodes 17-20.

Document of Constantine Arc
Index III episodes 1-3.

Battle Royale Arc
Index III episodes 4-6.

Dream Ranker Arc (Doppelganger)
Railgun T episodes 21-25.

Acqua of the Back Arc
Index III episodes 7-9.

British Royal Family Arc
Index III episodes 10-14.

DRAGON Arc
Index III episodes 15-17.

World War III Arc
Index III episodes 18-25.

Note: The Dream Ranker Arc is split into 2 entries because it covers multiple time periods. You can ignore Dream Ranker Arc (Introduction) and view Dream Ranker Arc (Indian Poker) as episodes 16-20 if you'd like.

AEGC Interest Stack index: https://myanimelist.net/forum/?topicid=2017008

I recommend the (simplified) chronological order over the release order

(watching by the actual chronology means switching series every few episodes... sorry, I'm too lazy for that)