Each city/town has it's own ordinances. It will completely depend on where you live. You can contact your town's building department and they can guide you if you are doing the work yourselves. If you are hiring a GC; they should handle any necessary permits for you.

The permit requirements vary from state to state and city to city. The primary purpose is to make sure that all renovations are done correctly and to current code for safety and longevity reasons.

In some places, you don't need a permit to take down a non-loadbearing wall -- it is considered a non-structural, cosmetic change. But if you are changing electrical or plumbing lines (not fixtures), you will probably need a permit.

If you are using a general contractor, s/he will pull the necessary permits.

Also...Do not let any contractor tell you that permits are not needed.

You may be able to find out more information through your jurisdiction's website.

In 99% of all locations in the US, you will need to file an engineer's report with your locality in order to prove that the wall is non load bearing, as well as for the electrical and HVAC that is in the wall that will need to be moved. As previously mentioned, you need to visit your local codes office yourself to familiarize yourself with your location's exact requirements and fees. There are often pretty onerous fees plus the requirement to open up the walls in order to make the already accomplished work visible to the codes officers should you skip the permitting process and someone turn you in.

Lucky for me, I live in the 1% that does not require much of anything.

We had to get a permit for the addition, but other than pay for it, didn't have to submit anything at all about what we were doing. We just told them we wanted to add on to the back of the house, paid $50 and headed home.

Needed nothing for the rest of the project, which included just about rebuilding the house, New roof, new siding, new windows and doors, all new wires from the pole on, and all new water/septic from the incoming meter (including a new septic system).

So like others have said, it can vary wildly what you need to do depending on where you live. We still made sure everything we did was up to code and all that. No reason to do substandard work just because no one is going to look at it to make sure we did it correctly. After all, this is where we live and we want it to last.

I don't think it has been made clear what can happen if you are required to get permits, but choose not to.

First, your locality may get wind of your project. This is unlikely if you are just swapping out light fixtures, but a major reno is obvious and they certainly can and do find out about it. Sometimes inspectors see it from the street, and often annoyed neighbors will rat you out. They can do this long after your project is finished.

If this happens, you may get a stop work order. No further work can proceed, regardless of whether you have no heat, your home is currently exposed to the elements or intruders because it's the day before the windows are installed, or if a hurricane is coming but the roof hasn't gone on yet. No one cares. No more work, full stop.

Next the city will demand to inspect before work resumes. If you are far enough along, you may get a tear-out order. That is, if your drywall, tile and cabinets are already up, they will get sledgehammered out. There is no choice or alternative on your part, you just do it--paying the cost of the demo, and then the cost of putting it all back up again. Of course, if an addition is involved but no building inspector has seen it, it may need to come down. The whole thing. Yes, I've seen it happen.

Through all of this you will be paying heavy fines, although towns may be lenient if you paid the GC to pull permits and they just pocketed the money instead.

Let's say you sneak by and finish your project without getting caught. You're all good now, right?

Wrong. If you have a kitchen fire and your insurance company discovers you have unpermitted electrical, your claim gets denied and you will be rebuilding your kitchen on your own dime.

If you avoid any major catastrophes, you could still face a big problem when you go to sell your house. Buyers can go to town hall and see whether your renovations were permitted or not. Your deal could fall through, buyers could insist on massive price reductions (your lack of permitting would now need to be disclosed to future buyers by your agent, if these buyers walk away) and you could now get hit by nice fat fines from your town.

Now, some towns are a little ridiculous about permitting. They require permits for every little thing, and often are very lazy about actually inspecting anything. So it's no wonder people feel ripped off in these cases. However, when it comes to a major renovation, the town absolutely has an interest in ensuring they are done up to code. People in the future are entitled to buy or rent a house with confidence that the whole thing won't fall down on their head.

Thanks all - I really appreciate your responses. This has helped us a lot.

I second Marcolo's comments. Sometimes it can be burdensome to get all of the permits pulled and complete inspections, but it's worth it for all the reasons enumerated. I'm glad we've always done that.

Of course, there are times when I wish we could just bypass the process and go ahead without the permits/inspections when we know what we're doing. I think I find them to be a bother when WE are the ones doing the renovations, but I want EVERYONE ELSE to get them so, if I end up buying their home, hopefully everything has been done properly. Can't have it both ways---so I'm glad our community requires permits and inspections along the way. I realize, of course, that it is not a guarantee that everyone does so.

"Sometimes it can be burdensome to get all of the permits pulled and complete inspections, but it's worth it for all the reasons enumerated."

And depending on the jurisdiction you want the contractor to pull the permits.
This makes them responsible for the work (as in they can lose their licenses) and in some places gives you access to a fund if the contractor fails to complete the work.

"If you have a kitchen fire and your insurance company discovers you have unpermitted electrical, your claim gets denied and you will be rebuilding your kitchen on your own dime."

As the owner you are insured against your own mistakes, including not getting a permit and burning down the kitchen.

The insurance companies like permits since it gives them an easily identified entity they can go after to recover from, that likely has insurance of their own.
If you read your insurance policy it will not have an exclusion for you making mistakes.

And many jurisdictions do not require any permits for simple things like changing a light fixture for one of the same overall watt rating, or replacing a switch or receptacle.

Some places are real PITA though, and will revoke the Certificate of Occupancy (CO) for the house when it is sold. They will the reinspect before issuing a new CO.
Anything they find that appears unpermitted they can require to be torn out or exposed so the work can be inspected.

Some New England states are notorious for this.

Everyone is absolutely spot on; however, I would add that all homeowners should make a point of going down to city/town hall before the project begins and find out what requirements will be needed, who (GC, electrician, plumber, septic, fire department for smoke detectors, etc.) should be expected to apply for each certificate, etc. and how long it takes to receive all of the above. Keep it in your notebook and then you have control of the information and the timeline. I have found that each town in my area (North of Boston) has slightly different interpretations and/or embellishments of the building code and each inspector has his own "rules" and his own time frame. Knowing these facts will make you life ever so much easier!