More than 131,000 students began their Leaving and Junior certificate examinations this morning.
After two years of severe disruption, this year marks the first full return to traditional written June exams.
The exams begin, however, amid continuing uncertainty as to when Leaving Certificate results will be made available.
The State Examinations Commission (SEC) has said a number of significant factors are making it impossible to determine a results date at this stage.
It said a shortage of teachers to mark exam papers is one of those factors and it has appealed to teachers to undertake "this vital work" this summer.
The fact that both Leaving and Junior Certificate papers need to be corrected this year has added to the pressure to secure enough teachers to mark papers over the coming months.
Pressure was also felt yesterday as teachers supervising exams were obliged to queue for several hours to collect examination papers and other materials at distribution centres in Dublin.
The SEC acknowledged the delays, which led to traffic congestion in areas around several centres.
For students beginning Leaving Certificate exams a number of measures aimed at mitigating the impact of the pandemic on their learning remain in place.
They have also been given a guarantee that aggregate results this year will be no lower than last year's.
The SEC said this commitment is also a factor in causing a delay and uncertainty as to the date of the publication of results.
It said extra time will be needed for additional analysis of marking outcomes and quality assurance.
Today also sees a return of Junior Certificate exams after two years when they were cancelled for all but a very small number of adult learners and early school leavers.
As a result, a small number of Leaving Certificate students are sitting a State exam for the first time. These are students who chose to skip the transition year.
Figures show 63,383 students intend sitting Leaving Certificate exams. They include 3,173 Leaving Certificate Applied candidates.
Meanwhile, 68,048 have applied to sit Junior Certificate exams.
There will be a deferred sitting of the Leaving Certificate exams in the first half of July for students who develop Covid-19 or symptoms of Covid-19 during the June exams.
The SEC said it has not yet finalised a timetable for these deferred sittings, which will be determined based on demand. The deferred exams will be held at a limited number of centres in schools regionally.
The SEC said criteria and requirements for access to the deferred sitting will be strictly applied and will have regard for the principles of equity, fairness and integrity.
It said it is too early to quantify the number of candidates who may need to sit deferred exams in July, and that this too is contributing to difficulty in determining a date for results.
However, it said it "will make every effort to mark the examinations and process the results as quickly as possible" and that a date for those results will be announced "as soon as possible".
A record number of candidates are due to sit the examinations this year. The rise is as a result of demographic growth. There has been a 6% rise in numbers registered to sit the exams compared to the last time a full set of tests was run in 2019.
A series of adjustments have been made to Leaving Certificate exam papers, in recognition of the challenges and difficulties that many students have faced over the past more than two years of their education. This included school closures. The adjustments have been designed to reduce the load for students and to help ensure that they are not disadvantaged.
For both Leaving and Junior Certificate students, the exams began this morning with English papers.
Wishing candidates luck, Minister for Education Norma Foley said that over the past two years students had proved themselves to be resilient, focused and determined.
Commenting on this year's acute shortage of examiners, Ms Foley said that "for a variety of reasons people may be making decisions as to how they wish to spend the summer".
However, she said she had every confidence that the SEC would be in a position to meet the challenge.