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ISM stands for "Industrial, Scientific, Medical", the designation given to several radio frequency bands available for use without a license if certain conditions are met (see ISM specifications). Since one of the requirements is the use of spread spectrum technology, this market is also referred to as "unlicensed spread spectrum".
Parts 15 and 16 of the United States Federal Communications Commission (FCC) regulations allow for the use of three Industrial-Scientific-Medical frequency ranges:
 902 to 928 MHz
2400 to 2483 MHz
5725 to 5860 MHz
A new band, called the Unlicensed National Information Infrastructure Band (U-NII), was created in the US in January 1997. This band covers 300 MHz of spectrum at 5.15-5.35 GHz and 5.725-5.825 GHz, and limits output powers to 12.5 mW/MHz. The complete technical specification for this band can be found on the  Apple website; a history of Apple's proposal can be found on the Warpspeed website.
The lower portion of the NII band includes radio frequencies already earmarked in Europe for local area wireless networks ("wireless LANs") adhering to a network standard called HIPERLAN. The upper portion lies within the existing 5.7 GHz ISM band.
Bands available for unlicensed use in other parts of the world are typically clustered near 2.4 GHz. Representative allocations are as follows:
| Geography | Frequency | Max Power Level |
| | [MHz] | [Watts] |
| U.S. | 2400-2483 | 1.0 |
| Europe | 2400-2483 | 0.1 |
| Japan | 2471-2497 | 1.0 |
Since there are relatively few constraints on the radio designer to use these bands, there are as many design approaches as there are designers. As such, there are no "standard" systems. Portable applications tend to use the same products as do cellular, PCS, or portable phone handsets. Non-mobile applications can use practically any product, depending on design. Since the majority of the systems being designed have a consumer focus, the emphasis is often on inexpensive SMT plastic-packaged devices.
In the US systems have predominately been built to operate in the 900 MHz band, where technology that has been developed for the cellular marketplace can be easily applied. This has led to enough crowding and background noise that users interested in data transfer (e.g. LAN designers) are currently working predominantly in the 2.4 GHz band to lessen interference (however this band has a problem with interference from microwave ovens). Where possible, PCS technology is stretched up in frequency and applied to these systems. The 5.8 band remains relatively unpopulated due to the significantly higher cost of applicable radio components.
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