Appraisal is a service performed, by an appraiser, that develops an opinion of value based upon the highest and best use of real property. The highest and best use is that use which produces the highest possible value for the property.

This use must be profitable and probable. Also of importance is the definition of the type of value being developed and this must be included in the appraisal, ie fair market value, condemnation value, quick sale value, etc. For improved residential property, this value is most often reported on a standardized form, the Uniform Residential Appraisal Report.

There are several types and definitions of value sought by a real estate appraisal. Some of the most common are listed:

• Market Value – Market value is usually interchangeable with fair market value or fair value. The legal definition of market value is usually given by some variant of the following: "The most probable price at which a property would trade in an arms-length transaction in a competitive and open market, in which the buyer and seller each act prudently and knowledgeably and in which the price is not affected by any special relationship between them".

• Value-in-use – The net present value (NPV) of a cash flow that an asset generates for a specific owner under a specific use. Value-in-use is the value to one particular user, which may be above or below the fair market value of a property.

• Investment value - is the value to one particular investor, which may be above or below the fair market value of a property.

• Insurable value - is the value of real property covered by an insurance policy. Generally it does not include the site value

Types of ownership interest

• Fee simple value - the most common type of value sought. It is the fair market value of the fee simple interest in a property unencumbered by any external factors such as existing leases.

• Leased fee value - is probably the second most common value opinion sought. It is the property owner's interest in a property that is encumbered by existing long term leases which may be at, below, or above prevailing market trends.

• Leasehold value - is the lessee's interest in a leased property.

Three approaches to value
There are three usual approaches to determining the fair market value of a property: cost approach, sales comparison approach, and income approach. The appraiser will determine which of the approaches is applicable and develop an appraisal based upon information from each individual market area.

Cost approach
The Cost approach is sometimes called the summation approach. The theory is that the value of a property can be estimated by summing the land value and the depreciated value of any improvements. It is the land value, plus the cost to reconstruct any improvements, less the depreciation on those improvements.

Sales comparison approach
The sales comparison approach looks at the price or price per unit area of similar properties being sold in the marketplace. Simply put, the sales of properties similar to the subject are analyzed and the sale prices adjusted to account for differences in the comparables to the subject to determine the fair market value of the subject. This approach is generally considered the most reliable, IF good comparable sales exist.

Income capitalization approach
The income capitalization approach, often simply called the income approach, is used to value commercial and investment properties. This approach capitalizes an income stream into a present value. This can be done using revenue multipliers or single-year capitalization rates of the net operating income. The Net operating income (NOI) is gross potential income (GPI), less vacancy (= Effective Gross Income) less operating expenses (but excluding debt service or depreciation charges applied by accountants).Alternatively, multiple years of net operating income can be valued by a discounted cash flow analysis (DCF) model. The DCF model is widely used to value larger and more expensive income-producing properties, such as large office towers.

Automated valuation models
Automated valuation models (AVMs) are growing in acceptance. These rely on statistical models such as multiple regression analysis and geographic information systems (GIS). While AVMs can be quite accurate, particularly when used in a very homogeneous area, there is also evidence that AVMs are not accurate in other instances such as when they are used in rural areas, or when the appraised property does not conform well to the neighborhood.