Is Circumcision Necessary for Conversion?
Question

A lawyer in Argentina is asking about the ruling on circumcision for a disbelieving man or woman who wants to enter Islam.
Praise be to Allah.Thank you for submitting this question. The issue of circumcision is one of the issues which in several cases forms a barrier for some of those who want to enter the religion of Islam. The matter is easier than many people think. 
Male circumcision in Islam
As for circumcision, it is one of the symbols of Islam. It is part of sound human nature (fitrah), and is part of the way of Ibrahim (peace be upon him). Allah, may He be exalted, says (interpretation of the meaning): “Then We revealed to you, [O Muhammad], to follow the religion of Abraham, inclining toward truth.” [an-Nahl 16:123]
The Prophet (blessings and peace of Allah be upon him) said: “The prophet Ibrahim (peace be upon him) circumcised himself when he was eighty years old…” (Narrated by al-Bukhari, 6/388)
Is male circumcision mandatory in Islam?
Circumcision is obligatory for a Muslim man, if he is able to do it. If he is not able to do it, such as if he fears that he may die if he is circumcised, or if a trustworthy doctor has told him that it will lead to haemorrhaging that may cause his death, then he is exempt from circumcision in that case, and he is not sinning if he does not do it.
Is circumcision necessary for conversion to Islam?
It is not appropriate under any circumstances to let the issue of circumcision be a barrier that prevents a person from entering the faith; rather the soundness of a person’s Islam does not depend upon him being circumcised. A person’s entering the religion of Islam is valid even if he does not get circumcised .
With regard to the issue of female circumcision, you will find the answer in question no. 427  .
I ask Allah to enable you to do all that is good and to protect you from all that is evil.
And Allah knows best.