Firstly: Upon Whom it is Wajib
The charity of Fitr is wajib upon every Muslim, male or female, young or old, free or enslaved. Consensus has been quoted over this by Ibn Rushd and Ibn Qudamah.
Secondly: The Financially Constricted at the Time Fitr Charity is Wajib
The Fitr charity is not wajib upon the financially unable at the time it is wajib. Consensus has been quoted on this by: Ibn al-Mundhir and al-Ramli.
Thirdly: The Degree if Financial Ability Where Charity Becomes Wajib
The Fitr charity is wajib upon every Muslim who has enough to give after what is given to himself and dependents, even if he does not own a nisab.  Except the Hanafis, who considered it a condition that the person giving charity has left a nisab after he gives the Fitr charity. This is since charity is not given unless there is a degree of wealth owned which is limited by ownership of a nisab, as well as the fact that it is an annual charity, so the nisab ought to be considered in it like other forms of legal charity. This is the position of the Malikis,  It is sufficient for the Malikis that, after giving the charity, he owns what suffices him and his family on the day of Eid only; unlike the Shafi`is and Hanbalis who condition that he have enough for the day as well as that night. Shafi`is, Hanbalis, and a group of the Salaf.
Fourthly: Delayed Debt and Fitr Charity
A debt that is delayed in repayment does not invalidate the giving of the Fitr charity. This is by agreement of the four schools of jurisprudence.
A condition for the Fitr charity is freedom, so the slave need not give it himself. This is by agreement of the four schools of jurisprudence.
Sixthly: The Ruling of a Father Giving the Fitr Charity on Behalf of His Young Children
The Fitr charity is wajib upon a father on behalf of his young children if he is able. Consensus has been quoted on this by: Ibn al-Mundhir, Ibn `Abd al-Barr, Ibn Rushd, and Ibn Qudamah.
Seventhly: The Ruling if a Master Giving Fitr Charity on Behalf of His Slave
It is wajib for the master to give the Fitr charity on behalf of his slave if able to do so. Consensus has been quoted on this by Ibn al-Mundhir, Ibn Rushd, Ibn Qudamah, relayed by al-Nawawi as the view held by all scholars except Dawud.
Eighthly: Giving the Charity of Fitr on behalf of the Wife
Scholars have differed over whether it is necessary to give the Fitr charity on behalf of the wife. This is according to two views:
The first: is that it is wajib for the man to give it on behalf of his wife if able. This is the position of the majority: Malikis, Shafi`is, and Hanbalis.
The second: is that it is not necessary upon him to do so. It is upon the woman to pay it for herself. This is the position of the Hanafis, Zahiris, Sufyan al-Thawri, chosen by Ibn al-Mundhir, Ibn `Uthaymin, and al-Qaradawi.
Ninthly: Charity for the Embryo
There is no charity payable on behalf of the embryo. This is by agreement of the four schools of jurisprudence, and it is the position of the majority of scholars.