Today, four different kinds of tags are commonly used. They are categorized by their radio frequency according to the following: low-frequency tags (between 125 kHz to 134 kHz), high-frequency tags (13.56 MHz), ultra-high frequency (UHF) tags (868 MHz to 956 MHz), and microwave tags (2.45 GHz). RFID tags can be further classified as either active or passive. An active RFID tag requires its own power source (battery) to operate, whereas passive RFID tags are powered by the signal generated from the reader device. With no on-board power supply, passive tags are oftentimes quite small.

Passive tags have practical read ranges that vary from about 10 mm up to about 6 meters.

In contrast, active RFID tags have practical ranges of tens of meters, and a battery life of up to several years. They also have longer ranges and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver.

Because passive tags are much cheaper to manufacture and do not depend on a battery, the majority of RFID tags on the market are passive in nature. Despite this cost advantage, factors like accuracy and reliability will continue to make the use of active tags more commonplace.