In Call of Duty: Modern Warfare a Killstreak is earned when you acquire a certain number of kills in a row without dying. The reward that your recieve will depend on how long the Killstreak lasts. Check out our Multiplayer Killstreak Rewards guide to see what those rewards are.
3 Kills - Personal Radar
Escort drone that enables the radar for the owner, and pings nearby enemies.
4 Kills - Counter UAV
A drone that constantly emits a scrambling signal, disabling enemy mini maps and incrementally disrupting their senses the closer they get to it.
4 Kills - UAV
UAV recon ship that enables the map for all allies, and reveals enemy locations.
4 Kills - Care Package
Call in a random killstreak care package to your location.
5 Kills - Cluster Strike
Signal for a number of cluster mortars to hit the designated location.
5 Kills - Cruise Missile
Control a long range missile with boost capabilities.
5 Kills - Precision Airstrike
Cal in twin jets for a precision strike along the best available path.
7 Kills - Wheelson
Remote controlled UGV with a powerful airburst turret.
7 Kills - Infantry Assault Vehicle
A manned light infantry vehicle with a .50 cal machine gun on top.
8 Kills - Emergency Airdrop
Call in 3 random killstreak care packages to your location.
8 Kills - VTOL Jet
Releases an initial missile barrage before guarding a location of the player's choice.
10 Kills - Chopper Gunner
Control an assault chopper armed with a turret and air to land missiles
10 Kills - White Phosphorus
Cover the battlefield with white smoke flare canisters that will disorient the enemy, and burn any of that wander too close.
11 Kills - Support Helo
Call in a heavy assault helo with twin turrets to patrol the map.
12 Kills - Gunship
Heavy assault gunship with three types of armaments.
12 Kills - Advanced UAV
Orbital UAV that reveals the enemy's direction on the mini map.
15 Kills - Juggernaut
Call in a care package that contains the Juggernaut assault gear.
Improve your chances of getting a long Killstreak by checking out our How to get the Best Weapons guide.