Safety and security will be the priority for race officials and local and federal law enforcement agencies at Monday's running of the Boston Marathon.
There will be a record number of participants this year with 36,000 runners.
Here are some guidelines that runners must follow.
There will no bags allowed in certain areas at or near the start in Hopkinton, as well as at or near the finish line in Boston.
A gear check opportunity on Boston Common will be available on the morning of the marathon only, allowing official participants to have a change of clothing for the conclusion of the race that can be stored in a bag provided by race officials at number pickup.
As for the allowable items for official participants, runners may carry the following items on race day: fanny packs (no larger than 5 inches by 15 inches by 5 inches) to carry food, nutritional products and personal items; standard manufactured "fuel belt" (bottles must be 1 liter or smaller); and armbands, which can carry a cellphone or small camera.
The use of headphones is discouraged, but permitted
Prohibited items for runners on race day are backpacks, any similar item carried over the shoulder, or handbags of any size; glass containers; costumes covering the face, and props.
This year's marathon is expected to attract about 1 million spectators, who will also have to follow new policies and restrictions along the route.
The overall message from law enforcement is, "If you see something, say something."
Thousands of uniformed and undercover officers will be patrolling the 26.2 mile course, and there will be an undisclosed number of security checkpoints.
Because of that, officials are strongly encouraging people to avoid bringing certain items to the race, including backpacks and over-the-shoulder bags, any coolers, glass containers or cans, bulky handbags or packages, large blankets or sleeping bags, and costumes that cover the face or extend out from the body.
"We are urging spectators along all 26.2 miles to carry personal items in clear plastic bags," said Kurt Schwartz of the Massachusetts Emergency Management Agency.
The Boston Athletic Association has a complete list of guidelines on its website.