The Sermon On The Mount
One segment of the sermon (Matthew 5:3-12; Luke 6:20-26) explains who will be blessed, or joyful (and in Luke, who will experience woe). That segment is called the Beatitudes and is often addressed specifically. We have a page on the Beatitudes.
The Sermon on the Mount is recorded in Matthew, chapters 5 to 7. It is often seen as the greatest teaching the world has ever received.
There is another version in Luke 6:17-49 which, interestingly, was preached on a "level place" or plain. Presumably, Jesus repeated this teaching more than once.