Why doesn't my Audi A5's engine start when I turn the key?

I have recently encountered an issue where my Audi A5 won't start when I turn the key in the ignition. The dashboard lights and radio turn on, but the engine won't start. What could be causing this issue and how can I fix it?

First and foremost, always check your car's battery before assuming the worst. It could be low on charge or even dead, causing the engine to not start. If the battery is not the issue, then it could be a faulty ignition switch or starter motor.