The 5x5

The 5x5 is known among bodybuilders and weightlifters for many years and is used by both old-school and the more "up to date" power lifters and bodybuilders.

Basic principles

In some variations it is recommended to start from 3x3 in other - the first two sets have a lighter weight, but warm-up sets don't count. In some variations the first session of the same exercise is heavy and then the second is 10-20% lighter (ie. squats on Monday are heavy and squats on Friday are lighter).

Duration: 

You can find many variations of the program, but generally it is completed in 12 weeks.
Weight: a weight that allows the athlete to perform 5 reps, and to have "grind" rep left in the tank, as most people will get weaker as the sets go by.
Nutrition: The routine is aiming for an increase in strength so there isn't anything special.
Who is it for?: Anyone that has completed a beginner routine. Even elite athletes cycle this routine.

The Routine (Bill Starr variation)

Its aim is power, so its around basic compound exercises. There are several options depending on the experience of the trainee: full body or a split. Best known today is the old variation of Bill Starr.
Many people call it the most perfect routine ever devised, it is indeed an amazing routine and it really requires minimal equipment.So let's get to it!
Original Bill Starr routine:

Monday – Heavy

• Power cleans – 5 sets of 5 (same weight)
• Bench – 5 sets of 5 (same weight)
• Squats – 5 sets of 5 (same weight)

Wednesday – Light

• Power cleans – 5 sets of 5 (15-20% less weight)
• Incline Bench – 5 sets of 5(15-20% less weight)
• Squats – 5 sets of 5 (15-20% less weight)

Friday – Medium

• Power cleans – 5 sets of 5 (ramp up weight)
• Overhead press – 5 sets of 5 (same weight)
• Squats – 5 sets of 5 (ramp up weight)

(example of ramping up: Let's say your goal weight is 120, 1st set: 80, 2nd: 90, 3rd:100, 4th:110, 5th:120)

The Bill Starr Power Routine

Monday – Heavy Day

• Squat – 5 sets of 5
• Bench – 5 sets of 5
• Powerclean – 5 sets of 5
• Weighted hyper extensions – 2 sets
• Weighted sit-ups – 4 sets

Wednesday – Light Day

• Squat – 4 sets of 5
• Incline Bench – 4 sets of 5
• High Pulls – 4 sets of 5
• Sit-ups – 3 sets

Friday – Medium

• Squat – 4 sets of 5, 1 triple, 1 set of 8
• Bench – 4 sets of 5, 1 triple, 1 set of 8
• Powercleans – 4 sets of 5, 1 triple
• Weighted Dips – 3 sets of 5-8
• Triceps and Biceps – 3 sets of 8 each

Bill Starr’s Beginner 5×5

Monday (Heavy Day – 85%)

Back Squats: 5 x 5 Ramping weight to top set of 5 reps across 5 sets
Bench Press: 5 x 5 Ramping weight to top set of 5 reps across 5 sets
Deadlifts: 5 x 5 Ramping weight to top set of 5 reps across 5 sets

Wednesday (Light Day – 65-70%)

Back Squats: 5 x 5 using 60% of Monday’s weight
Bench Press: 5 x 5 using 60% of Monday’s weight
Pullups: 5 x 5 Ramping weight to top set of 5 reps across 5 sets

Friday (Medium Day – 70-85%)

Back Squats: 5 x 5 using 80% of Monday’s weight
Bench Press: 5 x 5 using 80% of Monday’s weight
Rows: 5 x 5 Ramping weight to top set of 5 reps across 5 sets

The Bill Starr Strength Factor Routine

Monday (Heavy Day)

Back Squats: 5 x 5 ramping to limit
Bench Press: 5 x 5 ramping to limit
Deadlifts: 5 x 5 ramping to limit or Bent-Over Rows: 5 x 5 ramping to limit
Incline Dumbbell Press: 2 x 20
Calf Raises: 3 x 30

Wednesday (Light Day)

Back Squats: 5 x 5 (15-20% less) or Lunges: 4 x 6 ramping to limit
Good Mornings: 4 x 10 or Stiff-Leg Deadlifts: 4 x 10
Standing Overhead Press: 5 x 5 ramping to limit
Dips: When you can do 20 reps, start adding weight and drop the reps back to 8
Curls: 3 x 15

Friday (Medium Day)

Back Squats: 5 x 5 (10% less)
Incline Bench Press: 5 x 5 ramping to limit
Shrugs: 5 x 5 ramping to limit or Clean High Pulls 5 x 5 ramping to limit
Straight Arm Pullovers: 2 x 20
Chins: 4 sets to failure

Bill Starr’s “Big 3″ Program

Monday – Heavy Day

Powerclean – 5 sets of 5
Bench – 5 sets of 5
Squat – 5 sets of 5

Wednesday – Light Day

Powerclean – 5 sets of 5
Benchpress – 5 sets of 5
Squat – 5 sets of 5

Friday – Medium

Powerclean – 5 sets of 5
Benchpress – 5 sets of 5
Squat – 5 sets of 5

Recommendations and FAQ

If for example I'm doing my 5x5 bench press, I've finished 3 sets with the same weight, I'm too tired to use the same weight and hit 5 reps on the 2 sets that are left, do I reduce the weight or what?

Do 5 sets with the same weight if you can do all 5 sets with the same weight and complete 5 reps on each one - increase the weight .If for example, you do 5-5-5-4-3, stay on the same weight until you can do 5-5-5-5-5
Another variation is to count in the warm-up sets, so you've really got 3 heavy sets.

What do you mean by "Triceps and Biceps" etc.?

If the exact exercise is not stated, then it's assistance work, and here you can pick whatever exercises you want, like for example for Triceps you will pick 3 sets of triceps pull downs, and for Biceps you will pick 3-4 sets of Standing Biceps Curls.Assistance work should not be done in the 5x5 fashion, it should be more like 3x8-10.

When should I increase the weight?

Let's say you just started the routine.
It's your first week, It's time for you to bench press and you put 80kg on the bar.
You manage to hit 5-5-4-4-3
Second week.You hit 5-5-5-4-3
Third week.You got only 5 hours of sleep, and it's been a long day, you hit 5-4-4-3-2.It's okay it happens.
Forth week:Feeling good, you hit 5-5-5-5-5
Fifth week:You put another 2.5/5kg on the bar thus increasing the weight on the bar.

You stay on your new weight until you can do 5x5 and then you increase the weight again.

Suitable for a beginner with a few months of experience?

In my opinion this routine is for someone that has finished the typical 3 month~ novice programs, whether that would be be SS or something else, then at least a couple of months with a split.After that point a person can consider specializations.
As I've shown earlier there is an actual beginner variation of the 5x5, so you might want to look into that as well.

What about people with years of experience in the gym?

5x5 works, but for a person that has been training for a long while, expetially for strength, completing the required parameters could become be close to impossible without an immense stress on the CNS,  please take this into consideration.

For example, for someone deadlifting two or even three times his own body weight, such a load could be deadly. So power lifters with years of experience should look for a more appropriate routine or, in the worst case, at least don't deadlift with the 5x5 parameters, pyramid your weight up so you've got only one actual working set.

Mostly advanced athletes already know what works for them, and what does not.They're all different, one thing doesn't work for everyone, so it's their job to know their body well enough to extract the "core" from a particular routine and then build up their training around it, as opposed to blindly following the routine as its presented.

Test out your one rep max or even better your five rep max on each exercise.

If you don't know what your 1RM/5RM are, it would be useful if you'd test them out first, and then begin the routine.Or you could allow some flexibility in your first week, so you can actually test them out, and then start using the actual parameters of the routine.

Warming up:

I see this all the time, it just makes me cringe every time I see a guy that just walked in the gym, heads directly to the bench, puts 100kg/225lbs on the bar, and starts his set and I can hear his joints snapping and cracking while being with my headphones on and linger as he finishes his 3rd rep with his ass off the bench barely locking it out.
Make sure you warm-up your joints and the muscles you're going to be working before starting any of your working sets, let's say you're going to do flat bench, warm up your shoulders with some reverse flies and shrugs, warm-up your elbows, and do a set of chest flies all with really light weight, just so you get some blood flow to those muscles and get them ready, then do a few reps with lightweight on the bench, and then proceed to your working sets.
Not only will it help you avoid injuries but it will also increase your ability to lift heavier weight.

(sources:bbteam.com, stronglifts.com)