ESP8266 is a highly integrated chip designed for the needs of a new connected world. It offers a complete and self-contained Wi-Fi networking solution, allowing it to either host the application or to offload all Wi-Fi networking functions from another application processor.

ESP8266 has powerful on-board processing and storage capabilities that allow it to be integrated with the sensors and other application specific devices through its GPIOs with minimal development up-front and minimal loading during runtime. Its high degree of on-chip integration allows for minimal external circuitry, and the entire solution, including front-end module, is designed to occupy minimal PCB area.

Features

SDIO 2.0, SPI, UART
32-pin QFN package
Integrated RF switch, balun, 24dBm PA, DCXO, and PMU
Integrated RISC processor, on-chip memory and external memory interfaces
Integrated MAC/baseband processors
Quality of Service management
I2S interface for high fidelity audio applications
On-chip low-dropout linear regulators for all internal supplies
Proprietary spurious-free clock generation architecture
Integrated WEP, TKIP, AES, and WAPI engines
Solutions

Supports APSD for optimal VoIP applications
Patented spurious noise cancellation algorithm for integration in SOC applications
Supports Bluetooth co-existence interface
Self-calibrated RF to ensure optimal performance under all operating conditions
Zero factory tuning
No external RF components
Specifications

802.11 b/g/n
Wi-Fi Direct (P2P), soft-AP
Integrated TCP/IP protocol stack
Integrated TR switch, balun, LNA, power amplifier and matching network
Integrated PLLs, regulators, DCXO and power management units
+19.5dBm output power in 802.11b mode
Power down leakage current of <10uA
Integrated low power 32-bit CPU could be used as application processor
SDIO 1.1/2.0, SPI, UART
STBC, 1×1 MIMO, 2×1 MIMO
A-MPDU & A-MSDU aggregation & 0.4ms guard interval
Wake up and transmit packets in < 2ms
Standby power consumption of < 1.0mW (DTIM3)

Help your development more easy.
ESP8266 Serial WIFI Module Communite Forum>> Detail about ESP8266

1. High quality & low price
2. LWIP agreement
3. Support 3 modes: AP, STA, AP+STA
4. Perfect and simple AT commands

>>>>Translate data sheet

>>>>Some translated document

>>>>Turial

Now your Arduino can get on WiFI without braking the bank.
Use this module for your next Interet of Things project, home automation, Or remote sensor project.
This module adats the ESP8226 IC for use over a serial connection using simple AT commands.
No SPI interface or Know-How is required.

Warnings:
This module requires a 3.3 volt supply for VCC, and 3.3V logic. It is not 5V tolant. Connect RX or TX on 5V Arduino will
destroy this module. You must use a logic level converter, or a 3.3V Arduino

The 3.3V supply on the Arduino Uno has inadequate current capabilit to power this module. You must provide a separate,
higher 3.3V supply(about 300mA or better)

The ESP8225 module is very new on the market and support and documentation for it is currently very limited.