In what order should I watch Flash and Arrow TV Shows?

Question

The two TV shows Arrow and The Flash cross over (or so I'm told).

I've only been watching Arrow so far, and Barry Allen has just turned up. Do I need to start watching Flash episodes?

What order do I need watch these shows in?

Answer 1

Ideally, you should watch them in the order they aired. That is, if you want to get the most coherent story from both shows, you should watch Arrow up through the end of Season 2, then watch alternate episodes of The Flash Season 1 and Arrow Season 3. There is only one time when the shows seem to be significantly out of sync, and it won't make a whole ton of difference. In particular, watching in this order is the easiest way to guarantee not to spoil anything from either show by watching the other.

The second season of Arrow contains what is essentially a two-part pilot episode for The Flash, where a mundane Barry Allen comes to Starling City as a forensics expert; the end of that Arrow episode sets up the first episode of The Flash.

The first episodes of The Flash Season 1, and Arrow Season 3, take place at the same time, and there are cross-over cameos at the end of those episodes. Otherwise, the crossover events all seem to fall roughly in line with the order the episodes aired (e.g. crossovers that start on The Flash finish the next night on Arrow, or take place roughly between the previous and next episodes of the other show.)

So, watching in date-aired order is (almost) always going to work best for getting the entire story exactly as it was intended.

---

However, if watching them in air-date order is difficult (e.g. you're watching on Netflix or DVD where jumping between shows is tedious) you don't need to watch the episodes interleaved get the full story. In fact, there is at least once case where that will be a bit confusing: the timelines of the two series remain mostly in sync with each other for the first 2/3 or the season, but sometime between episodes 9 and 15, Arrow pulls ahead of Flash. If you're interested, there's a very spoilery explanation here:

In between which episodes of Arrow did this episode of Flash happen?

So, if you prefer watching one show at a time, you really only need to pay attention to the places where the stories meet. I've put together a quick comparison of the timelines of the shows and where they cross. For the episodes in between the cross-over points, you can watch each series straight through if you want. You will miss out on a bit of Easter-Egg-level details, where the shows occasionally refer to each other's ongoing plots, but nothing central ot particularly spoilery (that I know of.)

However, you'll want to make sure you're caught up on both shows at the cross-over points, or you'll not only be confused, but probably spoil something for yourself in the process. For example, characters from Arrow reveal key aspects of Arrows's season 4 plot up to that point when they show up on Season 1 of Flash.

Flash       Arrow    Crossover
~~~~~       ~~~~~    ~~~~~~~~~

S01E01 <--> S03E01   Same scene appears at the end of both episodes.
   .           .
   .           .
   .           .
S01E04 <--     .     Felicity Smoak visits Barry at some indeterminate point
   .           .
   .           .
   .           .
S01E08 <--     .     Two-part crossover, starts on *Flash*, end on *Arrow*
   .    --> S03E08
   .           .
   .           .
   .        S03E15
S01E18 <--     .     Crossover on *Flash* between episodes 15/16 of *Arrow*
   .        S03E16
S01E19 <--     .     Crossover on *Flash* between episodes 16/17 of *Arrow*
   .        S03E17
   .           .
   .   <--  S03E19   Crossover on *Arrow* between episodes 20/21 of *Flash*
   .           .
   .           .
   .           .     
S01E22 <--> S03E23   *Arrow* episode 23 appears to take place "during" *Flash* episode 22.


S02E01      S04E01
  .           .
  .           .
  .           .
S02E08 <--    .      Two-part crossover, begins on *Flash*, ends
  .     --> S04E08   next day on *Arrow*; also counts as back-door
  .           .      pilot for *Legends of Tomorrow*.

NOTE: The arrows indicate the "direction" of characters crossing from one show to the other
Which is usually character from *Arrow* going to *The Flash*. 

Answer 2

this question 'Arrows'ed my curiosity. Copy into notepad, save as CSV, import into Excel. You'll have a watch order list in a Flash... sorry.

Show, Series NO., Episode Name, Original Airdate
Arrow, 1, Pilot, October 10 2012
Arrow, 2, Honor Thy Father, October 17 2012
Arrow, 3, Lone Gunmen, October 24 2012
Arrow, 4, An Innocent Man, October 31 2012
Arrow, 5, Damaged, November 7 2012
Arrow, 6, Legacies, November 14 2012
Arrow, 7, Muse of Fire, November 28 2012
Arrow, 8, Vendetta, December 5 2012
Arrow, 9, Year's End, December 12 2012
Arrow, 10, Burned, January 16 2013
Arrow, 11, Trust but Verify, January 23 2013
Arrow, 12, Vertigo, January 30 2013
Arrow, 13, Betrayal, February 6 2013
Arrow, 14, The Odyssey, February 13 2013
Arrow, 15, Dodger, February 20 2013
Arrow, 16, Dead to Rights, February 27 2013
Arrow, 17, The Huntress Returns, March 20 2013
Arrow, 18, Salvation, March 27 2013
Arrow, 19, Unfinished Business, April 3 2013
Arrow, 20, Home Invasion, April 24 2013
Arrow, 21, The Undertaking, May 1 2013
Arrow, 22, Darkness on the Edge of Town, May 8 2013
Arrow, 23, Sacrifice, May 15 2013
Arrow, 24, City of Heroes, October 9 2013
Arrow, 25, Identity, October 16 2013
Arrow, 26, Broken Dolls, October 23 2013
Arrow, 27, Crucible, October 30 2013
Arrow, 28, League of Assassins, November 6 2013
Arrow, 29, Keep Your Enemies Closer, November 13 2013
Arrow, 30, State v. Queen, November 20 2013
Arrow, 31, The Scientist, December 4 2013
Arrow, 32, Three Ghosts, December 11 2013
Arrow, 33, Blast Radius, January 15 2014
Arrow, 34, Blind Spot, January 22 2014
Arrow, 35, Tremors, January 29 2014
Arrow, 36, Heir to the Demon, February 5 2014
Arrow, 37, Time of Death, Febuary 26 2014
Arrow, 38, The Promise, March 5 2014
Arrow, 39, Suicide Squad, March 19 2014
Arrow, 40, Birds of Prey, March 26 2014
Arrow, 41, Deathstroke, April 2 2014
Arrow, 42, The Man Under the Hood, April 16 2014
Arrow, 43, Seeing Red, April 23 2014
Arrow, 44, City of Blood, April 30 2014
Arrow, 45, Streets of Fire, May 7 2014
Arrow, 46, Unthinkable, May 14 2014
Flash, 1, Pilot, October 7 2014
Arrow, 47, The Calm, October 8 2014
Flash, 2, Fastest Man Alive, October 14 2014
Arrow, 48, Sara, October 15 2014
Flash, 3, Things You Can't Outrun, October 21 2014
Arrow, 49, Corto Maltese, October 22 2014
Flash, 4, Going Rogue, October 28 2014
Arrow, 50, The Magician, October 29 2014
Arrow, 51, The Secret Origin of Felicity Smoak, November 5 2014
Flash, 5, Plastique, November 11 2014
Arrow, 52, Guilty, November 12 2014
Flash, 6, The Flash Is Born, November 18 2014
Arrow, 53, Draw Back Your Bow, November 19 2014
Flash, 7, Power Outage, November 25 2014
Flash, 8, Flash vs. Arrow, December 2 2014
Arrow, 54, The Brave and the Bold, December 3 2014
Flash, 9, The Man in the Yellow Suit, December 9 2014
Arrow, 55, The Climb, December 10 2014
Flash, 10, Revenge of the Rogues, January 20 2015
Arrow, 56, Left Behind, January 21 2015
Flash, 11, The Sound and the Fury, January 27 2015
Arrow, 57, Midnight City, January 28 2015
Flash, 12, Crazy for You, February 3 2015
Arrow, 58, Uprising, February 4 2015
Flash, 13, The Nuclear Man, February 10 2015
Arrow, 59, Canaries, February 11 2015
Flash, 14, Fallout, February 17 2015
Arrow, 60, The Return, February 18 2015
Arrow, 61, Nanda Parbat, February 25 2015
Flash, 15, Out of Time, March 17 2015
Arrow, 62, The Offer, March 18 2015
Flash, 16, Rogue Time, March 24 2015
Arrow, 63, Suicidal Tendencies, March 25 2015
Flash, 17, Tricksters, March 31 2015
Arrow, 64, Public Enemy, April 1 2015
Flash, 18, All Star Team Up, April 14 2015
Arrow, 65, Broken Arrow, April 15 2015
Flash, 19, Who is Harrison Wells?, April 21 2015
Arrow, 66, The Fallen, April 22 2015
Flash, 20, The Trap, April 28 2015
Arrow, 67, Al Sah-him, April 29 2015
Flash, 21, Grodd Lives, May 5 2015
Arrow, 68, This Is Your Sword, May 6 2015
Flash, 22, Rogue Air, May 12 2015
Arrow, 69, My Name Is Oliver Queen, May 13 2015
Flash, 23, Fast Enough, May 19 2015

Answer 3

A more simplified list based on Rob D's post and kguest's comment post with what I believe to be the correct order to watch based on information from the answers. My main fix up was removing some episodes, since it had all of the first and second season of Arrow which are not exactly needed.

I also made it a little bit easier to read in this Google Spreadsheet. I did it for myself so I thought why not share it in case other people found the other posts too hard to read like myself.

The Flash, S01E01 — Pilot
Arrow, S03E01 — The Calm
The Flash, S01E02 — Fastest Man Alive
Arrow, S03E02 — Sara
The Flash, S01E03— Things You Can't Outrun
Arrow, S03E03 — Corto Maltese
The Flash, S01E04 — Going Rogue
Arrow, S03E04 — The Magician
Arrow, S03E05 — The Secret Origin of Felicity Smoak
The Flash, S01E05 — Plastique
Arrow, S03E060 — Guilty
The Flash, S01E06 — The Flash Is Born
Arrow, S03E07 — Draw Back Your Bow
The Flash, S01E07 — Power Outage
The Flash, S01E08 — Flash vs. Arrow
Arrow, S03E08 — The Brave and the Bold
The Flash, S01E09 — The Man in the Yellow Suit
Arrow, S03E09 — The Climb
The Flash, S01E10 — Revenge of the Rogues
Arrow, S03E10 — Left Behind
The Flash, S01E11 — The Sound and the Fury
Arrow, S03E11 — Midnight City
The Flash, S01E12 — Crazy for You
Arrow, S03E12 — Uprising
The Flash, S01E13 — The Nuclear Man
Arrow, S03E13 — Canaries
The Flash, S01E14 — Fallout
The Flash, S01E15 — Out of Time
The Flash, S01E16 — Rogue Time
The Flash, S01E17 — Tricksters
Arrow, S03E14 — The Return
Arrow, S03E15 — Nanda Parbat
Arrow, S03E16 — The Offer
The Flash, S01E18 — All Star Team Up
The Flash, S01E19 — Who is Harrison Wells?
Arrow, S03E17 — Suicidal Tendencies
Arrow, S03E18 — Public Enemy
Arrow, S03E19 — Broken Arrow
Arrow, S03E20 — The Fallen
The Flash, S01E20 — The Trap
Arrow, S03E21 — Al Sah-him
The Flash, S01E21 — Grodd Lives
Arrow, S03E22 — This Is Your Sword
The Flash, S01E22 — Rogue Air
Arrow S03E23 — My Name Is Oliver Queen
The Flash, S01E23 — Fast Enough

UPDATED TO INCLUDE Arrow S4 and Flash S2 Air Dates

The Flash, S201 - The Man Who Saved Central City (Air Date: 6-Oct-15)
The Arrow, S401 - Green Arrow (Air Date: 7-Oct-15)
The Flash, S202 - Flash of Two Worlds (Air Date: 13-Oct-1)
The Arrow, S402 - The Candidate (Air Date: 14-Oct-15)
The Flash, S203 - Family of Rogues (Air Date: 20-Oct-15)
The Arrow, S403 - Restoration (Air Date: 21-Oct-15)
The Flash, S204 - The Fury of Firestorm (Air Date: 27-Oct-15)
The Arrow, S404 - Beyond Redemption (Air Date: 28-Oct-15)
The Flash, S205 - The Darkness and the Light (Air Date: 3-Nov-15)
The Arrow, S405 - Haunted (Air Date: 4-Nov-15)
The Flash, S206 - Enter Zoom (Air Date: 10-Nov-15)
The Arrow, S406 - Lost Souls (Air Date: 11-Nov-15)
The Flash, S207 - Gorilla Warfare (Air Date: 17-Nov-15)
The Arrow, S407 - Brotherhood (Air Date: 18-Nov-15)
The Flash, S208 - Legends of Today (Air Date: 1-Dec-15)
The Arrow, S408 - Legends of Yesterday (Air Date: 2-Dec-15)
The Flash, S209 - Running to Stand Still (Air Date: 8-Dec-15)
The Arrow, S409 - Dark Waters (Air Date: 9-Dec-15)
The Flash, S210 - Potential Energy (Air Date: 19-Jan-16)
The Arrow, S410 - Blood Debts (Air Date: 20-Jan-16)
The Flash, S211 - The Reverse Flash Returns (Air Date: 26-Jan-16)
The Arrow, S411 - A.W.O.L. (Air Date: 27-Jan-16)
The Flash, S212 - Fast Lane (Air Date: 2-Feb-16)
The Arrow, S412 - Unchained (Air Date: 3-Feb-16)
The Flash, S213 - Welcome to Earth-2 (Air Date: 9-Feb-16)
The Arrow, S413 - Sins of the Father (Air Date: 10-Feb-16)
The Flash, S214 - Escape from Earth-2 (Air Date: 16-Feb-16)
The Arrow, S414 - Code of Silence (Air Date: 17-Feb-16)
The Flash, S215 - King Shark (Air Date: 23-Feb-16)
The Arrow, S415 - Taken (Air Date: 24-Feb-16)
The Flash, S216 - Trajectory (Air Date: 22-Mar-16)
The Arrow, S416 - Broken Hearts (Air Date: 23-Mar-16)
The Flash, S217 - Flash Back (Air Date: 29-Mar-16)
The Arrow, S417 - Beacon of Hope (Air Date: 30-Mar-16)
The Arrow, S418 - Eleven-Fifty-Nine (Air Date: 6-Apr-16)
The Flash, S218 - Versus Zoom (Air Date: 19-Apr-16)
The Flash, S219 - Back to Normal (Air Date: 26-Apr-16)
The Arrow, S419 - Canary Cry (Air Date: 27-Apr-16)
The Flash, S220 - Rupture (Air Date: 3-May-16)
The Arrow, S420 - Genesis (Air Date: 4-May-16)
The Flash, S221 - The Runaway Dinosaur (Air Date: 10-May-16)
The Arrow, S421 - Monument Point (Air Date: 11-May-16)
The Flash, S222 - Invincible (Air Date: 17-May-16)
The Arrow, S422 - Lost in the Flood (Air Date: 18-May-16)
The Flash, S223 - The Race of His Life (Air Date: 24-May-16)
The Arrow, S423 - Schism (Air Date: 25-May-16)