The Western concept of karma usually means instant retribution for bad behavior. If you steal money from your elderly grandma to buy a new car and immediately get in a wreck, that's karma catching up with you.
In Buddhism, karma is the universal law of "morally valenced" cause and effect [source: Jaffe]. Karma, in Sanskrit, means "action." Each of our actions, whether good or bad, carries a consequence. Some of the consequences of our actions are felt in this lifetime, although perhaps not as dramatically as the car example above. And other actions trigger consequences that, thanks to the continual cycle of death and rebirth, will ripple across lifetimes.
The Buddha understood karma not only as action, but the intention behind the action. Good or "skillful" actions are motivated by compassion, generosity, sympathy, kindness and wisdom, while bad or "unskillful" actions are driven by hatred, greed and delusion [source: BBC]. That's why there's such a strong emphasis in Buddhist teaching on mindfulness. Only by being fully aware of our motivations can we condition ourselves to act only on our best intentions and let negative thoughts simply pass by.
The karmic effects of our actions fall into two categories: psychological and universal [source: Jones]. Since reincarnation or transmigration is often a difficult concept for modern man to grasp, Buddhists tend to focus on the psychological consequences of karma. Treating people with kindness and generosity has the effect of lifting our spirits, while acting out of greed and envy darkens our minds and mood. In that way, the law of karma can certainly impact us in the here and now.
Traditionally, though, Buddhists understand karma as the universal law that determines the form that transmigration will take. It's our actions and decisions, not the divine judgment of a cosmic being, that determine where will be born among the six realms or planes of existence. While Buddhists don't believe in an eternal "soul" or "I" that continues from one like to the next, they do believe that our "patterns of mind" persist beyond death [source: Goldstein]. According to the rules of karma, you will be reborn in the plane that best matches your pattern of mind.
Truly despicable intentions could land you in one of the lowest realms of suffering, while perfect mindfulness and compassion could qualify you for the heavenly planes, or at least being born into a wealthy family. The rest of us will be reborn as animals or imperfect humans trying our best to move up, or at least not down, the karmic ladder.