Sister Julienne (Jenny Agutter)
The most experienced midwife at Nonnatus House, Sister Julienne is the consistent stalwart among the midwives.
Jenny was 18 when she played Roberta in the film of The Railway Children. Since then she's won a Bafta for her performance as Jill Mason in the 1977 film Eqqus and played Tessa Phillips in Spooks.
Sister Ursula (Dame Harriet Walter)
Joining the nuns for series six is Sister Ursula – a nun described as a “not very welcome addition” to the midwifery team.
Dame Harriet Walter is an accomplished star of the big and small screens, starring in Atonement, Sense and Sensibility, Downton Abbey, Little Dorrit and Star Wars: The Force Awakens.
Nurse Barbara Gilbert (Charlotte Ritchie)
Barbara is now an established face at Nonnatus House and is good friends with Trixie - despite becoming engaged to her ex-fiancé Tom.
Comedy fans will recognise Charlotte as Oregon from Channel 4's Fresh Meat and Hannah from BBC Three's Siblings.
Shelagh Turner (Laura Main)
Former nun Shelagh left Nonnatus House when she fell in love with and married Dr Patrick Turner, but missed the life at the convent and returned in series four to help out.
Laura first appeared on the stage at the age of 11 in a stage production of The Sound Of Music. As well as a lengthy career in theatre, she featured as DC Alison Bain in ITV's Murder City.
Nurse Phyllis Crane (Linda Bassett)
Officious Phyllis is not afraid to put ideas forward to try improve the lives of those at Nonnatus House.
Linda played Julia Roberts' mother in the film Mary Reilly, and was nominated for a Bafta for her performance as Ella Khan in East Is East. Past TV credits include BBC period dramas Sense and Sensibility and Lark Rise to Candleford, and in recent years she's starred in Calendar Girls and The Reader.