A portable or mobile toilet (colloquial terms: thunderbox, porta-john, porta-potty or porta-loo) is any type of toilet that can be moved around, some by one person, some by mechanical equipment such as a truck and crane. Most types do not require any pre-existing services or infrastructure, such as sewerage, and are completely self-contained. The portable toilet is used in a variety of situations, for example in urban slums of developing countries, at festivals, for camping, on boats, on construction sites, and at film locations and large outdoor gatherings where there are no other facilities. Most portable toilets are unisex single units with privacy ensured by a simple lock on the door. Some portable toilets are small molded plastic or fiberglass portable rooms with a lockable door and a receptacle to catch the human excreta in a container.

A portable toilet is not connected to a hole in the ground (like a pit latrine), nor to a septic tank, nor is it plumbed into a municipal system leading to a sewage treatment plant. The chemical toilet is probably the most well-known type of portable toilet, but other types also exist, such as urine-diversion dehydration toilets, composting toilets, container-based toilets, bucket toilets, freezing toilets and incineration toilets. A bucket toilet is a very simple type of portable toilet.

A chemical toilet collects human waste in a holding tank and uses chemicals to minimize the odors. Most portable toilets use chemicals in this way and therefore are considered chemical toilets. The chemicals may either mask the odor or contain biocides that hinder odor-causing bacteria from multiplying, keeping the smell to a minimum.

Enclosed portable chemical toilets are widely used for crowds at festivals, and for worksites without permanent toilets, such as early stages of construction and remote worksites.

On planes and trains, some toilets are chemical toilets, and others are vacuum toilets.

A portable camping toilet has a seat and a small waste tank. Adding a packet of chemicals to the waste tank reduces odors and bacteria, until the waste can be dumped at an appropriate facility. They are used in camping, travel trailers, caravans, and camper vans. They may also be used on small boats which lack a built-in marine toilet.

Waste aggregation and gelling (WAG) bags have a gel to immobilize liquid waste and surround solid waste in a plastic bag, which is then put in the trash. They are used in the US Army and in wilderness. They can be used to line a bucket, with a toilet-seat lid, and are required for Utah river trips.

Portable urine-diversion dehydration toilets are self-contained dry toilets sometimes referred to as "mobile" or "stand-alone" units. They are identifiable by their one-piece molded plastic shells or, in the case of DIY versions, simple plywood box construction. Most users of self-contained UDDTs rely upon a collection agency or a post-treatment process to ensure pathogen reduction. This post-treatment may consist of long-term storage or addition to an existing or purpose-built compost pile or some combination thereof. The necessity of a post-treatment step hinges upon the frequency and volume of use. For instances of infrequent or very modest seasonal use, a post-treatment phase might be deemed unnecessary due to the lower accumulation of waste, simplifying the overall disposal process.