When you say "Wi-Fi" today, you probably mean 802.11b, which is a subset of the general 802.11 standard. Most Wi-Fi devices that are currently in operation are using 802.11b. However, technology moves quickly, and 802.11g is gaining momentum fast.
The full 802.11b specification document is more than 500 pages long, but here are the key things to know about 802.11b:

• The 802.11b standard uses the 2.4GHz spectrum.
• The 802.11b standard uses a technology called Direct Sequence Spread Spectrum (DSSS) to minimize interference with other devices transmitting on the 2.4GHz spectrum.
• The 802.11b standard has a theoretical throughput speed of 11 megabytes per second (Mbps).

The 11Mbps speed compares favorably with the 10Mbps throughput of a conventional 10BASE-T wired Ethernet network, which may be what you are used to using at work. It is certainly faster than even the fastest broadband Internet connections.
However, for a variety of reasons Wi-Fi connections rarely achieve anything like its theoretical maximum (encryption slows 802.11b down, for one thing). Weak connectivity also slows Wi-Fi down. Even so, Wi-Fi connections should be fine for everyday uses such as file sharing or sharing an Internet connection. There may be some extremely demanding applications that Wi-Fi speeds are not good enough for, but I am hard put to think of any.
The most important thing you should take away regarding the speed of 802.11b Wi-Fi is that for most users 11Mbps is good enough. The 802.11b Wi-Fi connection is rarely slower than other parts of the system it is in, such as the network it is connected to, or access to the Internet.
I'll be telling you a little more about transmission speeds of 802.11b related to other wireless standards later in this article.The 802.11a and 802.11g Standards

The 802.11a and 802.11g standards are different variants of 802.11 that can be thought of as 802.11b's smarter, younger brothers. The 802.11a standard uses the 5GHz band for transmission, which minimizes the possibility of interference with the plethora of 2.4GHz devices out there (think microwaves, garage door openers, and so on) and promises a theoretic throughput of 24Mbps.
Still newer than 802.11a, 802.11g operates on the 2.4GHz spectrum and boasts throughput as fast as 54Mbps.
In other words, both 802.11a and 802.11g show the promise of being considerably faster than 802.11b.
The 802.11a standard poses some compatibility issues with 802.11b. But at least one vendor, Atheros Communications, makes 802.11a equipment that is backward- compatible with 802.11b. (Atheros also makes a "tri-mode" chipset that uses 802.11a, 802.11b, and 802.11g.) The chief advantage of 802.11a is that it will run into less interruption from other devices because it does not use the crowded 2.4GHz band.
Moving to 802.11a has some pluses and minuses, but moving to 802.11g is a no-brainer—because 802.11g systems are backward-compatible with 802.11b, and faster. This backward compatibility of 802.11g devices is a requirement for Wi-Fi certification.
Neither 802.11a nor 802.11g are starting to become mainstream, with prices a bit higher than for 802.11b. In fact, the 802.11g standard is replacing 802.11b as the standard for new equipment (it is preferred to 802.11a because of its backward compatibility). Pretty soon, 802.11g will be the de facto Wi-Fi standard that is at the "sweet" price point, and other, faster Wi-Fi standards—such as the proposed 802.11n—will be the new contender knocking at the door.The 802.11i Standard

The IEEE is in the process of developing a new security standard for 802.11 that is named 802.11i. The Wi-Fi Alliance has released a subset of the 802.11i standard that the Alliance has developed called "Wi-Fi Protected Access."
Products that successfully complete the Wi-Fi Alliance testing required for meeting its version of the 802.11i standard will be called "Wi-Fi Protected Access" certified.
Wi-Fi Protected Access provides a stronger level of encryption and authentication than is built into the current Wi-Fi standards. This means that Wi-Fi networks will be better protected from unauthorized access and other security problems. Wi-Fi Protected Access is intended to replace WEP encryption built into current Wi-Fi.
The new standard is also intended to be "software implementable." This means that current Wi-Fi products should be upgradeable to Wi-Fi Protected Access by running a software patch—new hardware will not be required.

Related Wireless Standards

You might also hear about some other wireless standards, and wonder how they are related to Wi-Fi. The two other wireless standards you are most likely to hear about are Bluetooth and 3G.
Bluetooth is a short-range connectivity solution designed for data exchange between devices such as printers, cell phones, and PDAs. Like 802.11b, it uses the 2.4GHz spectrum. Although Bluetooth is built into a great many devices, it is a standard with some severe disadvantages, mainly that it is far slower than 802.11b (with nominal throughput of up to 721 Kilobytes per second) and with a maximum range of about 30 feet (compared to Wi-Fi's unamplified range of several hundred feet). Bluetooth's main claim to fame is that it is inexpensive, which is why it has been added to so many devices.
3G is a catch-all term for a proprietary network using spectrums leased by telecommunications carriers such as Sprint and Verizon. Although 3G would undoubtedly transmit data at faster rates than Wi-Fi—perhaps at rates as fast as 384Mbps—there is no doubt that users would be expected to pick up the tab. (After all, it uses a leased spectrum that is not free for the telecommunications companies.)
At this point, there is very little in the way of completed 3G infrastructure, nor is there any reason to expect 3G technology to be used as the backbone for ad-hoc wireless networking in the way Wi-Fi has.

The Future of Wi-Fi

Wi-Fi is a disruptive technology that came unexpectedly and has been growing by leaps and bounds, mainly because it is inexpensive and fills a need. Originally, Wi-Fi was just a hack so that people could connect a notearticle to a network via wireless using a spectrum that didn't have to be paid for. No one expected it to grow so fast, and to become used so widely. The fact that it has spread like wildfire has caused many kinds of technology companies, from wireless cell phone providers to network hardware manufacturers, to rethink their businesses.
For sure, some telecommunications executives must be turning to each other and saying, "Hey, why should we build expensive proprietary networks when it is being done cheaply and on the fly using Wi-Fi?"

As Wi-Fi grows up, it is getting better, more secure, and faster. Clearly, vendors and the Wi-Fi Alliance have listened to the users' need for security (as represented by the 802.11i standard) and interoperability. If you decide to use one of the newer flavors of Wi-Fi, you'll probably find that it will interoperate well with older versions.