Best Man's Responsibilities

The best man is responsible for helping the groom prepare for the big day, from helping to choose the tuxedos to making sure he gets to the wedding on time.
Traditionally, the best man is a brother, relative or best friend of the groom.

Before the wedding

Arranges the stag party.
Select a gift for the groom
Arranges fitting sessions for ushers and groomsmen
Act as a liaison for the groom’s friends and family
He attends the rehearsal and rehearsal dinner.
Picks up the groom's formal wear prior to the wedding.
Confirm honeymoon travel arrangements.
Provide transportation for the groom to get to the ceremony and from the ceremony to the reception.

The morning of the wedding

Help the groom dress and finish packing
Insure that the car is packed for the honeymoon.
Has the wedding rings
Gathers all the travel tickets, passport, money/ travelers checks ID etc. together
Finishes final touches to his speeches
Any gifts or acknowledgments
Checkbook or credit card for any needed payments

Ensure that the groom:

Trouser zip is done up
Face and hair are groomed
If vows are written, that they are on him
Fear and second thoughts are calmed and put to rest
Uses the toilet
Shoes are tied
At the wedding

Transport the groom to the ceremony location.

Oversees ushers at the wedding.
Carry an extra copy of the ceremony seating plan in case the ushers need to refer to it.

Ensure the officiant's fee is delivered after the ceremony or at the rehearsal.

Sign the marriage certificate as a legal witness.

During the processional either stand at the front with the groom or proceed ahead of the groom. Walks with the maid of honor in the recessional.

The best man is responsible for safe keeping of the bride's wedding ring until it is time for blessing and exchange of the rings.

He helps to organize groomsmen for formal photographs.
At the reception

Sorts out the DJ or musicians
The best man is seated at the head table or a table of honor.

Dances with the bride and her attendants.

The best man is in charge of toasting during the reception. Reads out cards and special mail for the bride and groom

He makes sure that the groom has all tickets, hotel information, traveler's checks, itinerary etc. for the honeymoon.

Takes any clothes or other items that have been rented back to the hire shop. Gets suits cleaned and returned to the groom's home.

Expenses

The best man pays for his own formal wear and accessories.

If travel expenses are involved, he pays his own way, to the wedding, as well as hotel costs if necessary.

Gift for the bride and groom

Pay or help to pay for the stag party
Groom's emergency kit

Aspirin
Comb or hair brush
handkerchiefs
Hair gel
Extra toothbrush & toothpaste
Deodorant
Mouthwash

Check out these other articles in the Relationships category:

Date Your Spouse
Wedding Beauty Survival Tips
Meeting His Parents
Marrying Abroad Checklist
50 Ways To Show Your Love