For any web APPLICATION, browser automation and cross-browser testing are two critical testing activities to ensure that the software works on VARIOUS browsers/devices/platforms. Selenium[2] is a popular web automation tool that helps achieve that. It’s one of the most widely used and popular tools used in automation testing.

Advantages of Selenium:

• Open SOURCE: It’s developed in open and has excellent COMMUNITY support. The software is updated regularly, ensuring significant problems and bugs are fixed, and new features are getting added constantly. 
• Cross-Browser: Selenium allows you to run and test your web application in multiple browsers, such as Chrome, Safari, Firefox, ETC. 
• Cross-platform: You can use Selenium on Windows, Mac OS, or Linus. This allows testing the platform compatibility of your web application. 
• Language Agnostic: You can use Selenium in your favorite programming languages, such as Java, C#, Python, Ruby, and many more.

Disadvantages of Selenium:

• Learning Curve: One of the most common and recurring problems mentioned by new testers is that Selenium is complicated and takes a long time to learn. It requires prior programming knowledge. 
• No support for desktop/mobile: Selenium only supports web applications. You cannot use it to test your desktop and mobile applications. 
• No reliable tech support: As it’s open-source software, there’s no dedicated tech support that you can use in case you run into problems.
• Complicated debugging: It’s tougher to debug Selenium programs than the other tools and frameworks.