A timeshare is a type of vacation lodging usually located on or near a resort facility. They are very similar to vacation condominiums (see second homes); however, a timeshare is not sold as a single property. Instead timeshares are sold in weekly time slots or intervals and the timeshare unit is shared among potentially 52 different owners. Timeshares have been sold as fixed weeks, floating weeks, rotating weeks and most recently as vacation clubs or memberships as well as point based systems.

While the format of these transactions varies, they typically involve the purchase of one room or suite in a resort for a week a year, either on a long-term basis (30-99 years) or as actual registered (deeded) ownership in perpetuity. The costs are high: $18,000 (US dollars, 2006) or more up-front, followed by HOA (homeowners association) or maintenance fees of $500/year and up, which continue for as long as the voyager owns the timeshare.

The lawyerly details of what you get very widely:

• A deeded property indicates that you legally own a fractional interest in buildings or land, supposedly in perpetuity, including all liabilities.
• A "right to use" is not ownership; it's a long-term lease, paid up front, which continues decades into the future. It is often used in countries like Mexico where local law restricts foreigners from buying land.
• Another variation is to sell ownership not in the actual land (one "home week" in one specific room type, in one specific resort) but to sell an interest in the company or trust that owns or operates the resort.

The actual results vary just as widely:

• Fixed weeks were the original model, ownership of the same week each year at the same property. Most "legacy timeshare" properties – independent properties built by developers twenty or more years ago, sold off as individual timeshares and turned over to homeowners associations with no further involvement by the original promoters and no further sales effort – fall into this category.
• Rotating weeks (sometimes mislabeled "flex weeks") move each owner to a different week each year on a fixed schedule. Sometimes this lands in high season, sometimes this lands too far off-season to be of use, but in theory each owner get a prime time slot at least some of the time.
• Floating weeks are slightly more flexible; prospective owners buy a week a year in a specific season without committing up-front to specific dates (which can be chosen each year, subject to availability).
• Vacation clubs, memberships and point-based systems are offered by large chains with multiple properties; the buyer gets a certain number of "points" which may be redeemed for accommodation each year anywhere in the chain, but more desirable times and locations cost more points.

If you have time in a timeshare which you don't intend to use, there may be a few options:

• Some operators may be willing to rent your rooms to other voyagers, if the property is still advertising short-term hotel stays.
• You may be able to swap places with another traveler using a home stay network or hospitality exchange model if the location is desirable and the rules of your timeshare permit.
• Companies like Resort Condominiums International (RCI) and Interval International (II) act as brokers of timeshare exchanges, again subject to the rules of your timeshare.

Nonetheless, there is a risk – if what you are holding is simply a bad deal, no one will want to buy out your position and you will be left paying costly annual maintenance fees for a holiday property which you never use.

Then there's the question of what happens if the company operating these schemes goes bankrupt. In some of these schemes you still hold a property deed (with attendant liabilities of ownership), in others you may be left with nothing.

The promoters of these various schemes are quick to point out that these are most often cheaper (and less maintenance-intensive) than buying a full second residence, such as a cottage. A more meaningful comparison would be between timeshares and hotels or other rentals. If you're staying at the same place (or a property in the same group) for a week a year, every year, for a decade or more, you might break even on a timeshare. Maybe the rooms and facilities are better or more spacious than the standard rental you'd get for the money, but don't trust the promoter's comparisons.

Conversely, if this goes badly you may be stuck with a unit which no one wants to buy and which continues to accrue annual maintenance, property tax and HOA fees even when you're not using the facility. At worse, this is worth less than nothing – a liability instead of an asset – and you might not even be able to give away your ownership stake in a problematic timeshare property. The original promoter is under no obligation to take this back, even for free. There are plenty of elderly folk locked into €450–900/yr maintenance payments for timeshare holiday homes which they no longer use and are unable to sell.

A timeshare contract is a complex real estate transaction with many pitfalls. Don't sign one without expert advice.

For the traveller, a timeshare can be inflexible in that it represents a commitment to vacation at the same place (or a venue under the same ownership) one week a year, every year. This can be awkward in years when the traveller doesn't have a week free, can't afford to take a trip or would prefer to vacation elsewhere. A last-minute cancellation is likely to be difficult or impossible if there is a change in plans. Timeshares also carry a high up-front cost as they must be purchased in advance, not merely rented.

It's also difficult to predict whether a hotel which was a good place to stay this year will retain the same standards and the same market position in the future. Sometimes a property is renovated and upgraded, with a corresponding increase in prices; sometimes a property or destination goes into decline through years of neglect. Some once-popular vacation destinations have even become ghost towns. If what you got is a club membership, the decay can affect all the premises of the company – it may have financial difficulties or it may have stopped trying to attract new customers, or lures them under a new name.

Even if a property gets a major facelift or renovation, the owners of the timeshare will have to pay for that work in higher HOA/maintenance fees. Disbanding an association or converting an existing timeshare building to another purpose (such as apartments or condos) later may be awkward or impossible due to the fragmented ownership structure; it's difficult to get all owners to agree to a single course of action.

Like any other bet on the real estate market, the value of an individual timeshare may rise or fall over time. A timeshare should not be considered an investment; the resale value is far lower than the prices the original high-pressure salespeople promoted when the project was launched, if the timeshare can be sold at all. It can also be all but impossible to get out of some of these arrangements – even if a person is sick, elderly or bankrupt (and therefore unable to travel) the terms of the contracts vary widely on whether the promoters are under any obligation to voluntarily allow the unfortunate owner to leave the scheme.

Dubious tactics have been used to hard-sell timeshares. One unsolicited pitch claims the victim has won something for free – such as travel or accommodation – but with a few nasty surprises in the fine print; the offer contains more hidden charges than a "Nigeria 419" advance fee scam and the price of the supposed "freebie" is that the voyager is forced to sit through a lengthy, high-pressure sales pitch. These pitches may be packed with spurious claims that timeshares will inevitably increase in value and be easy to get out of at any time – which often isn't true.

In some cases, there are waiting lists of hundreds of people attempting to get out of unfavourable timeshare arrangements. To add insult to injury, some unscrupulous vendors advertise 'We can get you compensation for your timeshare' and then re-victimise the hapless voyager by subjecting them to yet another high-pressure sales pitch for yet another timeshare. In some cases, aggressive "hot room" tactics by which prospective victims are plied with alcohol and subjected to several hours of intensive sales pressure do violate local law. If you have been missold, have been told you cannot exit the scheme or you want compensation you can get legal advice, though that can cost money and there are no guarantees as to the outcome of legal action.

For the owners of hotels and resorts, timeshares represent a locked-in market and a lucrative source of capital. This may explain the eagerness of promoters of these schemes, as well as some of the high-pressure sales tactics. For the voyager, however, an unused timeshare may become a burdensome ongoing expense; in some cases, maintenance costs have increased 400% over the life of the contract.

If you must buy, it's usually cheaper to buy from a fellow voyager who is no longer visiting the property and looking to sell instead of buying directly from the original promoter.

• Second homes