The 3-4-1

Target Formation
The 11v11 formation that is mimicked by the 3-4-1 is the 3-5-2.

Positioning
The 3-4-1 features three fullbacks (one center half in the middle with a right and left outside back on either side), four midfielders (arranged in a diamond shape with a holding central midfielder [#6] at the base, an attacking central midfielder [#10] at the point, and two wide midfielders to the right and left), and one forward [#9] in the most advanced position on the field.

Attacking Philosophy
The forward in the 3-4-1 serves as the focal point of the attack, moving all over the attacking areas of the field and not staying in one place for very long. The attacking central midfielder and the two outside midfielders work with the forward to create angles of attack by which to exploit the opposing defense. The holding central midfielder is the primary distributor and ball possessor in a 3-4-1. In the attack, the holding midfielder moves the ball to dictate the direction of focus and drops in behind the attacking players in a supporting role. The three fullbacks provide support and release for the midfielders and forward. Occasionally, the outside fullbacks will make attacking runs along the wings, but this is less common than in a 3-3-2.

Strengths
When played well, the 3-4-1 is an effective attacking formation. The nearly constant movement of the forward and the advanced positions of the attacking center midfielder and the wide midfielders creates a very aggressive tactical approach. When the holding central midfielder pushes higher into the attack with possession, the movements of the attacking players become less predictable and more unexpected; this increases the pressure on the opposing defenders.

Weaknesses
Because the 3-4-1 features a diamond shape in the midfield, it is not a formation that promotes consistent ball possession. The space between the attacking and holding midfielders can be exploited for possession. 

When to Employ the 3-4-1
The 3-4-1 is an effective formation for teams with highly-skilled ball possessors who can play the holding central midfield [#6], attacking central midfield [#10], and center half positions and for teams with speedy, high-endurance players who can handle the nearly constant movement needed to maintain the attack. 

Derivatives of the 3-4-1

3-1-3-1
The 3-1-3-1 is a form of the 3-4-1 that promotes more ball possession in the attacking areas of the field by changing the diamond shape of the midfielders to a "T" shape. This is accomplished either by dropping the attacking central midfielder down to the level of the wide midfielders (more conservative) or by pushing the wide midfielders higher up to the level of the attacking central midfielder (more aggressive). In either alteration, the midfielders and forward are arranged into a diamond shape with the #6 at the base, the #9 at the top, and the #10 in the middle serving as the focal point of the attack. This diamond shape with the #10 in the middle promotes more ball possession by filling in the space between the #6 and the #10 that exists in the 3-4-1, but it is much more susceptible to counterattacks as it commits more players to higher positions on the field and demands a high degree of possession to be effective.