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The film is structured with two timelines: color sequences are alternated with black-and-white sequences. The latter are put together in chronological order. The color ones, though shown forward (except for the first one, which is shown in reverse), are ordered in reverse. Chronologically, the black-and-white sequences come first, the color sequences come next.

Using the numbering scheme suggested by Andy Klein—who took numbers from 1 to 22 for the black-and-white sequences and letters A–V for the color ones in his article for Salon magazine[4]—the plotting of the film as presented is: Opening Credits (shown "backward"), 1, V, 2, U, 3, T, 4, S, ..., 22/A, Credits.

There is a smooth transition from the black-and-white sequence 22 to color sequence A and it occurs during the development of a Polaroid photograph.

The chronological order of the story can be viewed as a "Hidden feature" on the 2-Disc Limited Edition Region 1 DVD and the 3-Disc special Edition Region 2 DVD. In this special feature the chapters of the film are put together into the chronological order and is shown: Ending Credits (run in reverse), 1, 2, 3, ..., 22/A, B, ..., V, then the opening title runs "backward" to what was shown (the opening title sequence is run in reverse during the actual film, so it is shown forward in this version).

Stefano Ghislotti wrote an article in Film Anthology which discusses how Nolan provides the viewer with the clues necessary to decode the plot as we watch and help us understand the chronology. The color sequences include a brief overlap to help clue the audience into the fact that they are being presented in reverse order. The purpose of the fragmented reverse sequencing is to force the audience into a sympathetic experience of Leonard's defective ability to create new long-term memories, where prior events are not recalled, since the audience has yet to see them.

Especially all the lies Leonard tells himself to create a sense of purpose and how he allows his condition and so many of the 'clues' he finds to misdirect him..
One thing i'd forgotton but which i still don't quite get was the clip when he is in bed with his wife and he clearly has his tattoos....

I'll tell you.

The first hour and half of the film is not real, you're in and watching somebody's dream, but you don't know you are, unless you already knew, which you do now.

Then the person who's dream you're in, wakes up, and the last half hour explains the dream you was watching, but you don't know that, unless you already knew, which you do now.

It is definitely one that you'd view with different eyes the 2nd time round knowing what the ending was. If we do watch it as one of these films I'll do you a proper review then, it's not fresh enough in my mind to do one now but it was one of my favourites of these types films