Becoming a Muslim requires a very simple act, but the meaning behind it is very deep.

You have to believe that there is only one God, Allah, who created the entire universe, and that Muhammad (peace be upon him) is his final messenger on earth.

أشهدُ أنْ لا إلهَ إلاَّ اللهُ وأشهدُ أنَّ محمّداً رسولُ الله

lā ʾilāha ʾillā-llāh, muḥammadun rasūlu-llāh

If you recite this, with total sincerity, you have become a Muslim. It really is as simple as that. It is recommended, though not required, to declare it in front of two witnesses, so that the Muslim community can recognize and welcome you.

Muslims call this recitation the Shahadah, and refer to it as the first Pillar of Islam.

And if you become a Muslim by converting (some Muslims would say `reverting` as you are going back to the religion you were born with) to Islam your fellow Muslims will accept you as if you had been born a Muslim.