creator is Staff PhotographerSeattle Post-Intelligencer, CC-BY. Image originally found here
The act of trick or treating has very fuzzy origins; no one really knows exactly where it started but it became a national phenomenon quite quickly around 100 years ago.
In addition to that, many other traditions, such as costumed kids going around the neighborhood for candy, apple bobbing (which has more or less faded from the present Halloween), and presenting a scary theme originated around this time.
Perhaps the first Halloween tradition began in the 1800's when a couple of Irish immigrants brought turnips and beets to America, where it caught on and evolved into a staple part of modern Halloween culture.
Click here for the origin of Halloween
Click here for the present tradtions of Halloween