Listen to the clips below of competitors' thoughts from 2015 and previous years.
The Australian Olympian leads the CIC3* for 8&9 year olds after an excellent Dressage test with Graf Liberty scoring 32.9.
The Oxfordshire based Irish rider lies in 2nd with Fenyas Elegance in the CCI3*, scoring 40.0.
Four time Blenheim winner Pippa Funnell has made an excellent start in the Dressage scoring 43.8 with her horse Or Noir de la Loge.
The GB Olympian is delighted with her start in the Dressage with her horse Beltane Queen, scoring 50.2.
The 25 year old Australian rider takes the lead in the CIC3* on Belcam Bear with a score of 35.4. Now based in the UK she was delighted with her test.
Charlotte Agnew is the leading British rider after day 1 of the CCI3* with her horse Out of Africa.
The American who is based in Britain makes an impressive start scoring 42.7 with Loughan Glen in the CCI3* on his return to Blenheim.
The Canadian rider is back at Blenheim and also competing for the first time in this country since the London Olympics. Phoenix has opened up with a score of 48.1 with Pavarotti.
4 times Blenheim Winner Pippa Funnell discusses her hopes with her horse Or Noir de la Loge.
Andrew Nicholson who won last years 8&9 year old class, discusses his prospects for the two main competitions this week.
Blenheim Palace Horse Trials Office: Blenheim Palace, Woodstock, Oxon, OX20 1PS Tel: 01993 813335