It is celebrated as a single joyful feast, indeed as the "great Lord's Day". Each Sunday of the season is treated as a Sunday of Easter, and, after the Sunday of the Resurrection, they are named Second Sunday of Easter, Third Sunday of Easter, etc. up to the Seventh Sunday of Easter, while the whole fifty-day period concludes with Pentecost Sunday.
Easter Sunday and Pentecost correspond to pre-existing Jewish feasts: The first day of Pesach (פסח) and the holiday of Shavu'ot (שבועות).In the Jewish tradition, the 49 days between these holidays are knows as Counting of the Omer (ספירת העומר). 
Since 2000 the Second Sunday of Easter is also called Divine Mercy Sunday. The name "Low Sunday" for this Sunday, once common in English, is now rarely used.
The solemnity of the Ascension of the Lord is celebrated on the fortieth day of Eastertide (a Thursday), except in countries where it is not a Holy Day of Obligation. In such countries it is celebrated on the following Sunday (the forty-third day of Eastertide). The days from that feast until the Saturday before Pentecost (inclusive) are days of preparation for the Holy Spirit the Paraclete.
Before the 1969 revision of the calendar, the Sundays were called First Sunday after Easter, Second Sunday after Easter, etc. The Sunday preceding the feast of the Ascension of the Lord was sometimes, though not officially, called Rogation Sunday, and when the Ascension had an octave, the following Sunday was called Sunday within the Octave of the Ascension, but when this octave was abolished in 1955, it was called Sunday after the Ascension. Pentecost was followed by an octave, which some reckoned as part of Eastertide.
When the Anglican churches implemented their own calendar reform in 1976, they adopted the same shortened definition of the Easter season as the Roman Catholic Church had promulgated six years earlier. In the Church of England, the Easter season begins with the Easter Vigil and ends after Evening Prayer (or Night Prayer) on the Day of Pentecost. Some Anglican provinces continue to label the Sundays between Easter and the Ascension "Sundays After Easter" rather than "Sundays of Easter"; others, such as the Church of England and ECUSA, use the term "Sundays of Easter".
- Easter Season Resource Library - Crossroads Initiative
- Normae Universales de Anno Liturgico et de Calendario
- French translation
- Writings on Easter, Eastertide and Lent liturgical days
- Liturgy of Hours of Eastertide