Wi-Fi is the most common standard communication model on the internet. It assumes that the device or object being connected to is capable of connecting to an IEEE 802.x network and therefore is able to handle IP-based networks.

There are many wi-fi capable devices available in the market. Some examples of Wi-Fi modules are the ExpressIf ESP-8266 and ESP-32 modules, Texas Instruments CC3200, Microchip ATSAMW25, Intel Edison, and Galileo. This is not the complete list of devices and there are many other combinations that combine a Wi-Fi capable controller and an MCU.

Wi-Fi modules are relatively cheap and are generally good options for when it's possible or desirable to use an available network and support high-payload transfers, given their reliability and connection speed (up to 6.7 Gbps).

A Wi-Fi-based IoT solution looks pretty much like the following diagram:

Multiple devices can connect to a node, such as a router, which in turn connects to the internet and allows connected devices to access the internet.