Surfing the web has moved from the stationary computers to mobile devices such as smartphones and tablets. As the technology moves further and more devices comes out on the market this is a trend that will continue. This makes it more important for web developers to adapt and make their websites fit not only for one device. The website needs to fit all devices. Since many of these devices are using wireless connections, the website performance has also become even more important in order to give the users a good experience.   Responsive web design is an approach for designing and developing web pages. By using the three techniques of flexible grid layout, flexible images and media, and media queries, websites can get a design that fits all devices. Responsive web techniques will also make the web page perform better on each device since it makes the web page adapt to its environment. There are several performance techniques that can be applied to a website in order to increase performance and loading time. Responsive web design including performance techniques can together make a great impact on a website's loading speed and user experience.   This thesis embraces this approach for web development. By developing a design theory, a website emerges where these approaches of web development have been implemented. During the development of the website the experiences implementing this approach and techniques is discussed. The website developed for this thesis was able to finish loading below 4 seconds on a mobile device using a 3G connection. We argue that responsive web design and performance techniques can help a website immensely to increase its user experience and performance.