Say who you are and why you are involved in the presentation. For example, you're the chairman of a university department hosting a conference in which several of your students will be presenting papers, or you're the head of a medical department at the hospital that will host a conference.
State your purpose, which is to offer an invitation to the presentation.
Outline what will be presented. Note any special preparations that participants are making. For instance, a group of scientists may, for the first time, be presenting conclusions based on experiments and data.
Note any special guests or ceremonies.
Explain why the recipient is being invited. For example, she may be a patron of the museum hosting the presentation, or he might be an alumnus of the university where your event will take place.
Ask recipients to RSVP by a specific date, and express your hope that they will attend.