The San Luigi Orders admit members solely by invitation and by recommendation from existing members. They are intentionally extremely selective and it is not possible for persons unconnected with the Orders and their membership to apply for admission.

Membership in an Order of Chivalry is rightly viewed as a mark of distinction, and this is all the more the case in respect of the San Luigi Orders since they are under the Royal Patronage of a reigning monarch. For this reason, candidates who are admitted are considered to have demonstrated merit through achievement, character and service. They are also expected to be active in their support of the Orders and the causes that they support.

The principal distinguishing factor in membership is that the Order of the Crown of Thorns is confined to baptised Christians (without regard to denomination) while the Order of the Lion and the Black Cross has no such religious requirement, and is open to non-Christians as well as to atheists and agnostics. Other than this, no discriminatory factors are applied in the consideration of nominees for membership.

The Companionates of the Orders are reserved for younger members who will, in due course, normally be promoted to Knight or Dame.

Where petitions for membership are declined, it is the policy of the Orders not to give reasons for rejection or to enter into discussion regarding the decision.

Promotion to a higher rank in the Orders is made by the Prince Grand Master in the case of those who have rendered distinguished service to the cause of San Luigi and/or Bunyoro-Kitara. Such promotion is purely discretionary and the majority of members will remain at the rank of Knight or Dame throughout their time in the Orders.