Obviously, the laws for towing trailers can get confusing, so we'll try to break them down.  First, let's get the bare necessities out of the way.  No matter where you are in the U.S. or Canada, you'll have to make sure the trailer you're towing is equipped with:
Tail lights: The trailer needs operable taillights for basic road safety.
License plate light: Make sure to clearly display your license plate with its own light.

There's also equipment that, aside from being common sense to have for safety, is also required in the vast majority of states:
Safety chains: These chains, which cross over in the shape of an X to connect the trailer to the towing vehicle, help prevent separation if the hitch connection fails.
Brake lights: Your trailer isn't transparent. The people behind you are already having enough trouble seeing around your trailer for stops ahead, so the trailer should have brake lights of its own to prevent a rear-end collision.
Clearance lights: These might be required only if your trailer exceeds a certain width.
Turn signals: If, for instance, your trailer blocks your vehicle's signal lights, it's good to have separate turn signal lights on the trailer.
Reflectors: These are an invaluable precaution to keep your large trailer visible.

Here is the current laws and restrictions at the time of post, you should verify with the local authorities before traveling.

[table]
[tr]
[td]State/Province[/td][td]Trailer Width[/td][td]Triple Tow[/td][td]Brake Laws[/td][td]Max Tow Speed[/td][td]Ride In 5th Wheel[/td][td]Ride in Pickup Camper[/td][td]Ride in Travel Trailer[/td][/tr]
[tr][td]United States[/td][/tr]
[tr][td]Alabama[/td][td]8'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]70 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Alaska[/td][td]8'6"[/td][td]yes[/td][td]5,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Arizona[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]75 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Arkansas[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]70 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]California[/td][td]8'6"[/td][td]yes[/td][td]1,500 lbs.[/td][td]55 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Colorado[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]75 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Connecticut[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Delaware[/td][td]8'6"[/td][td]no[/td][td]4,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]District of Columbia[/td][td]8'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Florida[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]70 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Georgia[/td][td]8'0"[/td][td]no[/td][td]1,500 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Hawaii[/td][td]9'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Idaho[/td][td]8'6"[/td][td]yes[/td][td]1,500 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Illinois[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Trailers are not permitted on boulevards in and around Chicago.[/td][/tr]

[tr][td]Indiana[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Iowa[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Kansas[/td][td]9'0"[/td][td]yes[/td][td]yes[/td][td]70 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Kentucky[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Lousiana[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]70 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Maine[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]Maryland[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]LP Gas is prohibited on I-95 tunnels of Baltimore Harbor and Fort McHenry. Alternate route for RVs with propane is over the Francis Scott Key Bridge on I-695.[/td][/tr]

[tr][td]Massachusetts[/td][td]8'6"[/td][td]no[/td][td]10,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td][/td][td][/td][/tr]
[tr][td]LP Gas is prohibited between Boston and East Boston; Sumner and Callahan tunnels; Prudential and Dewey Square tunnels.[/td][/tr]

[tr][td]Michigan[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]55 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Minnesota[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]70 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Mississippi[/td][td]8'6"[/td][td]yes[/td][td]2,000 lbs.[/td][td]55 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]Missouri[/td][td]8'6"[/td][td]yes[/td][td]NS[/td][td]70 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Montana[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Nebraska[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]75 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Nevada[/td][td]8'6"[/td][td]yes[/td][td]1,500 lbs.[/td][td]75 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]New Hampshire[/td][td]8'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]New Jersey[/td][td]8'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]On the New Jersey Garden State Parkway there is a 55' maximum length. For the New Jersey Turnpike or other roads call 908-247-0900 for specific towing regulations.[/td][/tr]
[tr][td]LP Gas prohibited between Manhattan and Jersey City in the Holland Tunnel. Between Manhattan and Fort Lee, the lower level of the George Washington Bridge (I-95 South) and George Washington Bridge Expressway. Between Manhattan and Weehawken in the Lincoln Tunnel.[/td][/tr]

[tr][td]New Mexico[/td][td]8'0"[/td][td]yes[/td][td]3,000 lbs.[/td][td]75 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]New York[/td][td]8'6"[/td][td]no[/td][td]1,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]LP gas is prohibited between Manhattan and Jersey City in the Holland Tunnel. Between Manhattan and Fort Lee, New Jersey lower level of the George Washington Bridge (I-95 South) and the George Washington Bridge Expressway between Manhattan and Weehawken, New Jersey: Lincoln Tunnel. LP gas is prohibited between Manhattan and Brooklyn on the Brooklyn Battery Tunnel and between Manhattan and Queens on the Queens Midtown Tunnel.[/td][/tr]

[tr][td]North Carolina[/td][td]8'6"[/td][td]no[/td][td]1,000 lbs.[/td][td]55 mph[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]North Dakota[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]70 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Ohio[/td][td]8'6"[/td][td]yes[/td][td]2,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Oklahoma[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Oregon[/td][td]8'6"[/td][td]no[/td][td]Not Stated[/td][td]55 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Pennsylvania[/td][td]8'6"[/td][td]no[/td][td]yes[/td][td]55 mph[/td][td]yes[/td][td][/td][td][/td][/tr]
[tr][td]Rhode Island[/td][td]8'6"[/td][td]no[/td][td]4,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]South Carolina[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]South Dakota[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]75 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Tennessee[/td][td]8'0"[/td][td]yes[/td][td]1,500 lbs.[/td][td]70 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]Texas[/td][td]8'6"[/td][td]yes[/td][td]4,500 lbs.[/td][td]70 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]LP Gas is restricted on the Washburn Tunnel between Pasadena and Galena Park on the Houston Ship Channel. Maximum of two 7 1/2 gallon containers (30 pounds gas each) or one 10-gallon container (40 pounds of gas) of DOT (ICC) approved type, with shutoff valve at discharge opening. Valve must be closed when in tunnel. LP gas as vehicle fuel is prohibited.[/td][/tr]

[tr][td]Utah[/td][td]8'6"[/td][td]yes[/td][td]2,000 lbs.[/td][td]75 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Vermont[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Virginia[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]55 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]RVs equipped with ICC-approved LP tanks, not exceeding two 45-pound capacity tanks (or two permanently mounted containers with a maximum total capacity of 200 pounds) may cross the Viriginia/Chesapeake Bay Bridge/Tunnel provided that, in the opinion of the toll collector or police officer after inspection, the tanks are completely shut off and securely attached.[/td][/tr]

[tr][td]Washington[/td][td]8'6"[/td][td]no[/td][td]3,000 lbs.[/td][td]65 mph[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]West Virginia[/td][td]8'0"[/td][td]no[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Wisconsin[/td][td]8'6"[/td][td]yes[/td][td]3,000 lbs.[/td][td]65 mph[/td][td]yes[/td][td]yes[/td][td][/td][/tr]
[tr][td]Wyoming[/td][td]8'6"[/td][td]yes[/td][td]Not Stated[/td][td]75 mph[/td][td][/td][td][/td][td][/td][/tr]
[tr]
[td]State/Province[/td][td]Trailer Width[/td][td]Triple Tow[/td][td]Brake Laws[/td][td]Max Tow Speed[/td][td]Ride In 5th Wheel[/td][td]Ride in Pickup Camper[/td][td]Ride in Travel Trailer[/td][/tr]
[tr][td]Canadian Province[/td][/tr]
[tr][td]Alberta[/td][td]Not Stated[/td][td]yes[/td][td]2000lbs[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]British Columbia[/td][td]Not Stated[/td][td]Not Stated[/td][td]1400kg[/td][td]Not Stated[/td][td][/td][td][/td][td][/td][/tr]
[tr][td]Manitoba[/td][td]Not Stated[/td][td]yes[/td][td]910 kg[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]New Brunswick[/td][td]Not Stated[/td][td]Not Stated[/td][td]yes[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Newfoundland/Labrador[/td][td]Not Stated[/td][td]Not Stated[/td][td]yes[/td][td]Not Stated[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]NW Territories[/td][td]Not Stated[/td][td]Not Stated[/td][td]1360kg[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Nova Scotia[/td][td]Not Stated[/td][td]yes[/td][td]1800kg[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Ontario[/td][td]Not Stated[/td][td]Not Stated[/td][td]1360kg[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Prince Edward Island[/td][td]Not Stated[/td][td]Not Stated[/td][td]1500kg[/td][td]Not Stated[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Ouebec[/td][td]Not Stated[/td][td]Not Stated[/td][td]1300kg[/td][td]Not Stated[/td][td][/td][td]yes[/td][td][/td][/tr]
[tr][td]Saskatchewan[/td][td]Not Stated[/td][td]yes[/td][td]1360kg[/td][td]Not Stated[/td][td]yes[/td][td]yes[/td][td]yes[/td][/tr]
[tr][td]Yukon[/td][td]Not Stated[/td][td]Not Stated[/td][td]910kgs[/td][td]Not Stated[/td][td]yes[/td][td]yes[/td][td][/td][/tr]

[/table]