This is the Stanford Encyclopedia of Philosophy entry on moral responsibility.

When a person performs or fails to perform a morally significant action, we sometimes think that a particular kind of response is warranted. Praise and blame are perhaps the most obvious forms this reaction might take. For example, one who encounters a car accident may be regarded as worthy of praise for having saved a child from inside the burning car, or alternatively, one may be regarded as worthy of blame for not having used one's mobile phone to call for (...) help. To regard such agents as worthy of one of these reactions is to ascribe moral responsibility to them on the basis of what they have done or left undone. (These are examples of other-directed ascriptions of responsibility. The reaction might also be self-directed, e.g., one can recognize oneself to be blameworthy). Thus, to be morally responsible for something, say an action, is to be worthy of a particular kind of reaction —praise, blame, or something akin to these—for having performed it.[1.. (shrink)