The longsword is considered by some to the symbol of the Western knight. Refered to by some as a 'bastard' or 'hand and a half sword', it remained an oft carried weapon by a knight or men at arms, even in times when he would rely primarily on other weapons in actual war.
The blade was sharpened on both edges and fencing masters would often teach strikes with the false or 'back' edge of the blade. The longsword typical retains a straight or near-straight crossguard even in ages when other guards were proving more suitable for combat. Many believe this has to do with the religious imagery of the cross the sword makes when viewed point down.
A number of period fechtbucher or fencing manuals have survived from fencing masters such as Talhoffer, Liechtenauer and Vadi allowing us to develop a reasonable understanding of actual combat techniques of this weapon, should one wish to do so.
Longsword vs Arming Sword
Separate to the longsword, but often confused with the same, is the weapon that has come to be known as the arming sword. The confusion is fostered by the reference in the popular roleplaying game Dungeons and Dragons and brought into recreationist societies by those that play the same. The primary (and some say only) difference is that the arming sword is used primarily used one handed (allowing the use of a shield or buckler) and the longsword is used primarily (some say only) with two hands precluding the use of a defensive device. This is because an arming sword's blade is shorter than the longsword, and the hilt typically lacks enough room to place both hands in a comfortable combat position.