The Pistols (also Twin Pistols or Dual Pistols) are Lara's standard weapons and reliable companions in many Tomb Raider games. She carries them in all the games from Tomb Raider I to Tomb Raider V - Chronicles, with the exception of the Ireland and VCI Parts in Chronicles, the first two levels of The Last Revelation and the few occasions when they've been taken away from her. After they've been dearly missed in The Angel of Darkness, they made their return in Tomb Raider Legend and since then have always been in the games.
Lara has unlimited ammo for these and will always carry two of them. They are not very effective, but most of the mortal opponents, except the skeletons and the mummies in The Last Revelation, can be killed with them. If you run and jump around a lot and circle your opponents they will suffice most of the time, even against a bigger opponent like the demigods or the T-Rex.
Because Lara is ambidextrous, she carries a pair of pistols, one for each hand. These were designed to be used as a pair--the left pistol actually ejects spent casings on the left side. In TR1-5, they are the weakest weapon in the game, requiring 20-30 rounds to kill an unprotected human enemy. Advertisements for TR3 describe her pistols as being 9-mm. Along with their visual similarity, this would suggest they were based on Browning Hi-power pistols. However, some FMVs also show her holding what looks like Colt 1911s or Desert Eagle pistols.
On Legend and Underworld, Lara uses the same USP .45 Match pistols as appeared in the films. On Legend, these had a 15-round capacity, upgradeable to 20. On Anniversary, she is carrying a pair of Colt Mark IV Series 80 pistols, which appear to be chambered in .357. Again, these have a 20-round capacity.