Is it illegal to copy an eBook?

Excuse me, but I've been wondering about something related to copyright law and digital media. Specifically, I'm curious if it's actually illegal to make a copy of an eBook, or if there are any specific circumstances under which it would be considered legal? I understand that traditional physical books often have copyright protections in place, but I'm not sure if the same rules apply to electronic versions of those works. Could you clarify the legality of copying eBooks for me?