The Education Minister has told students the exams are important but "just one pathway in education"
Almost 121,000 students have started their Leaving and Junior Certificate exams.
The numbers include 58,000 students sitting the Leaving Cert, while more than 5,000 exam centres are being opened across the country.
English is the first paper for all students, while those sitting the Applied Leaving have it combined with communications.
The first tests got under way at 9.30am this morning, with the Junior Cert Civic, Social & Political Education and Leaving Cert Home Economics, Scientific and Social exams taking place this afternoon.
This year is the first time that a new course in Politics and Society will be tested in 41 pilot centres, with the exam to be held on Wednesday 20th June.
Education Minister Richard Bruton wished students sitting exams "the very best of luck".
He said: "You have put in a huge effort to get to this point and you should be very proud of the work that you have put in.
"I’d like to remind everyone that although these exams are important, they are just one pathway in education. There are now a range of opportunities available to you to fulfil your ambitions."
ASTI President Ger Curtin urged students to 'keep things in perspective' during the exam weeks, saying: “While some level of anxiety is completely normal, it’s really important that you keep things in perspective. Exams are just one small aspect of life. They are not everything.
"Eat well, get plenty of rest, take exercise, build in relaxation time, organise yourself so that you have everything you need each day and so that you are not rushing to get to an exam in time.”
The state exams will run for more than two weeks, with the final Leaving Cert exams to take place on Friday 22nd June.