The Arduino Ethernet Shield allows an Arduino board to connect to the internet. It is based on the Wiznet W5100 ethernet chip (datasheet). The Wiznet W5100 provides a network (IP) stack capable of both TCP and UDP. It supports up to four simultaneous socket connections. Use the Ethernet library to write sketches which connect to the internet using the shield. The ethernet shield connects to an Arduino board using long wire-wrap headers which extend through the shield. This keeps the pin layout intact and allows another shield to be stacked on top.

The latest revision of the shield adds a micro-SD card slot, which can be used to store files for serving over the network. It is compatible with the Arduino Duemilanove and Mega (using the Ethernet library coming in Arduino 0019). An SD card library is not yet included in the standard Arduino distribution, but the sdfatlib by Bill Greiman works well. See this tutorial from Adafruit Industries for instructions (thanks Limor!).

Brand:	Tinkering Supplies
Brand Part Number:	4313
Our Part Number:	h4313