Both **“May I come in?”** and **“Shall I come in?”** are possible, but
they have slightly different meanings and tones.
### 1. **May I come in?**
= **Am I allowed to come in?**
It is primarily a request for **permission**.
> **May I come in?**
> — Yes, come in.
For example, a student knocks on the teacher's door:
> **Student:** May I come in, sir?
> **Teacher:** Yes, come in.
**May** is traditionally the most formal modal for asking permission.