When we develop web applications, we have the responsibility to ensure that our application works for any user and works for as many different devices as possible. In this talk, I discuss why it is important to pay attention to these requirements from the very beginning and not postpone them to a later point in time. I then jump into the technical side and share the practical tips and tricks that I have learned over the years to ensure that my applications are both responsive and accessible. Listeners should take away something both on the motivational side ("Why should I care about responsiveness and accessiblity?") as well as on the practical side ("How can I practically improve the accessibility and responsiveness of my site?").