The Diocese of Malolos (Latin: Dioecesis Malolosinae; Tagalog: Diyosesis ng Malolos; Spanish: Diócesis de Malolos) is a Latin Church ecclesiastical jurisdiction or diocese of the Catholic Church in the Philippines, encompassing the whole Province of Bulacan and Valenzuela City in metropolitan Manila and is a suffragan to the metropolitan Archdiocese of Manila. The mother church of the Diocese is the Cathedral-Basilica of the Immaculate Conception located in Malolos City, Bulacan. The Blessed Virgin Mary, under the title of Immaculate Conception is the principal patroness of the diocese.
 It was excised from the Archdiocese of Manila on December 11, 1961, by Pope John XXIII and was officially established on March 11, 1962, upon the installation of Manuel P. del Rosario, then-Bishop of Calbayog, by Salvatore Siino, the papal nuncio, as the first bishop of the diocese. Since August 21, 2019, the current and fifth Bishop of Malolos is Dennis C. Villarojo, who was appointed by Pope Francis on May 14, 2019.
 As the Church of Bulacan needed a diocese of its own, Pope John XXIII, on November 25, 1961, issued the Apostolic Constitution Christi fidelium, separating the Diocese of Malolos from the Archdiocese of Manila and establishing it as its suffragan. The present territory of the diocese is the civil province of Bulacan composed the cities of Baliwag, Malolos, Meycauayan and San Jose del Monte, and of the towns of Angat, Balagtas, Bocaue, Bulakan, Bustos, Calumpit, Guiguinto, Hagonoy, Marilao, Norzagaray, Obando, Pandi, Paombong, Plaridel, Pulilan, San Ildefonso, San Miguel, San Rafael, Santa Maria and Valenzuela City, formerly known as Polo, was later separated from Bulacan to be a component city of Metro Manila. Doña Remedios Trinidad was then created as a town for the portion near the Sierra Madre mountains.
 For the new diocese, Manuel P. del Rosario, then Bishop of Calbayog in Samar was appointed as the first Bishop of Malolos. He was jubilantly welcomed by the newly gathered Bulakeño faithful that now formed the diocese. Governor Tomas Martin and the provincial government of Bulacan were present. Del Rosario's canonical installation was presided over by then Apostolic Nuncio to the Philippines, Salvatore Siino. During his tenure, he established the Immaculate Conception Seminary (Minor) in 1962 at the Bulacan church convent, and was later transferred to the current seminary complex in Tabe, Guiguinto, Bulacan. Religious and monastic orders were soon invited to form communities here as Bulacan became a known producer of priestly and religious vocations. During this time, the diocese had eight (8) vicariates: Valenzuela, Malolos, Hagonoy, Sta. Maria, Baliuag, Meycauayan, Plaridel and San Miguel. In 1966, Del Rosario received Bishop Leopoldo A. Arcaira (+1994) as his auxiliary bishop. In 1971, Bishop Ricardo J. Vidal (who became Archbishop of Lipa, then Cebu) was appointed as coadjutor bishop due to Del Rosario's ill health.
 As Vidal was assigned as the new Archbishop of Lipa, Malolos was given a young and energetic bishop from Cavite, Cirilo Reyes Almario, Jr., who was appointed Apostolic Administrator sede plena of Malolos and then became the second Bishop of Malolos. Several developments would in fact occur during Almario's term. One of his most known is the establishment of the diocese's own major seminary, the Immaculate Conception Major Seminary. The Institute of Formation was established in 1983 with Fernando G. Gutierrez as first rector. The college department followed the next year and its theologate in 1987. ICMAS, as it is called, is Almario's greatest legacy. Today the seminary houses future priests not only from Malolos but from neighboring dioceses as well.
 In 1987, Almario headed the diocese's Silver Jubilee in celebration of its 25 years as a local church. Special jubilees were held during the event such as Jubilee Days for Men, Women, Children, Priests, Religious and Seminarians. On March 11, the diocese celebrated its anniversary date with much joy and festivity. Donations for the poor were also held on the next day and preparations for the diocese's first synod was held.
 On the occasion of the diocese's 25th anniversary, the first synod was held in June to July 1987, with the theme, "Prepare for the Lord a Perfect People" (Lk. 1:17) that was prepared by all the faithful as means of receiving the reform of the Second Vatican Council. Almario divided the aspects of Christian life and formed the WESTY (Worship-Evangelization-Service-Temporalities-Youth) formation. During this time, the diocese was again divided, adding another vicariate: St. Martin of Tours (Bocaue).
 With Almario's resignation in 1995, then Manila Auxiliary Bishop Rolando Octavus Joven Tria Tirona was appointed as the third Bishop of Malolos. Despite his short tenure, much of his pastoral work in the Bulacan local church involved fulfilling most of the plans Almario left of, part of which is the elevation of the Malolos Cathedral into a minor basilica. During this time, the tenth vicariate of the diocese was formed, San Jose del Monte.
 In December 1999, at the inauguration of the Great Jubilee Year 2000, the Diocese of Malolos witnessed the elevation of its cathedral as minor basilica granted by Pope John Paul II together with the episcopal coronation of its patroness, La Virgen Inmaculada Concepcion de Malolos.
 Together with the basilica at present, there are eight (8) more shrines in the diocese: the Parish of the National Shrine of Our Lady of Fatima, Valenzuela City (1976); the National Shrine and Parish of St. Anne, Hagonoy, (1991); the National Shrine of the Divine Mercy, Marilao; the Diocesan Shrine and Parish of Sagrado Corazon de Jesus, San Rafael (2000); the Diocesan Shrine of Mary, Mother of the Eucharist & Grace, Sta. Maria (2006); the Diocesan Shrine of Nuestra Señora de la Inmaculada Concepcion de Salambao, Obando (2007); the Diocesan Shrine of Mahal na Poon ng Krus sa Wawa in Bocaue (2008) and the Diocesan Shrine and Parish of St. John the Baptist, Calumpit (2013).
 In 2004, Jose Francisco Oliveros, then Bishop of Boac, replaced Bishop Tirona, who would later be assigned as Prelate of Infanta and then Archbishop of Caceres. Oliveros became Apostolic Administrator sede vacante before assuming office. It was in his term that the Diocese of Malolos prepared for its Golden Jubilee. During his time, the diocese was divided into four ecclesiastical districts (West, East, South and North).
 The diocese had five preparatory years dedicated to the priests, religious, laity and the youth of the Diocese. During the journey of the Diocese, the Jubilee Cross and the replica image of La Virgen Inmaculada Concepcion de Malolos joined the community in its journey towards the different religious, social, cultural and beneficial gatherings held during the five-year preparation, which was a remarkable opportunity for people to renew their faith in the Lord.
 The diocese fulfilled four jubilee projects: the Jubilee Shelter Program in Plaridel, Bulacan under the Commission on Social Action, for those who need homes due to the devastation of Typhoon Ondoy; the Diocesan Pastoral Center in Malolos City under the Diocesan Curia; the Diocesan Formation Center in Guiguinto, Bulacan, under the Commission on Formation for different seminars and events of the Diocese and the Bahay Pastoral in San Ildefonso, Bulacan, a home for retired and sickly priests.
 Oliveros remained in office until 11 May 2018 when he was received into the hands of the Creator. He is the first Bishop of Malolos to die in office. The Diocese of Malolos then came into sede vacante. Pope Francis assigned the diocese temporarily to the current Bishop of the Diocese of Cubao, Honesto F. Ongtioco, as the Apostolic Administrator of Malolos, from 11 May 2018 to 21 August 2019 upon the installation of the 5th and current bishop of Malolos, Dennis C. Villarojo.
 On May 14, 2019, Pope Francis appointed then Auxiliary Bishop of the Archdiocese of Cebu and Titular Bishop of Gisipa, Dennis C. Villarojo, as the fifth Bishop of Malolos. Villarojo once served as personal secretary to the late Cardinal Ricardo Vidal who was former Coadjutor Bishop of Malolos. He was canonically installed at the Malolos Cathedral-Basilica on August 21, 2019, by then Manila Archbishop Luis Antonio G. Tagle and Apostolic Nuncio, Gabriele G. Caccia, marking a new chapter in the history of the Diocese of Malolos.
 In February 2020, Pope Francis granted the canonical coronation of the image of La Purisima Concepcion in Santa Maria, Bulacan and in September 2021, he also granted the diocese a new minor basilica, the Minor Basilica of La Purisima Concepcion, Santa Maria, where the image is enshrined.
 On March 11, 2022, the Diocese celebrated its 60th Anniversary with a Mass presided by the Apostolic Nuncio to the Philippines, Charles John Brown Also in the ceremonies were the two surviving bishops of Malolos, Dennis Villarojo, and Caceres Archbishop Rolando Tria Tirona, and bishops who served or came from the Diocese.
 On February 27 up to March 2, 2023, the diocese hosted the 29th Canon Law Society of the Philippines [CLSP] National Convention.
 VICARIATE OF THE IMMACULATE CONCEPTION
 VICARIATE OF ST. ANNE
 VICARIATE OF ST. JAMES THE APOSTLE
 VICARIATE OF ST. AUGUSTINE
 VICARIATE OF ST. MICHAEL THE ARCHANGEL
 VICARIATE OF ST. MARTIN OF TOURS
 VICARIATE OF SAINT JOSEPH
 VICARIATE OF LA PURISIMA CONCEPCION
 VICARIATE OF ST. FRANCIS OF ASSISI
 VICARIATE OF SAN DIEGO DE ALCALA
 The current Bishop of Malolos is Dennis C. Villarojo. He was appointed by Pope Francis on May 14, 2019, to succeed the late bishop, Jose F. Oliveros who died last May 11, 2018 due to cancer. He was installed as the fifth Bishop of Malolos on August 21, 2019, by Luis Antonio G. Tagle, then Archbishop of Manila as the metropolitan bishop of the diocese, and Gabriele G. Caccia, then Apostolic Nuncio to the Philippines as the representative of the Pope. Prior of his appointment as Bishop of Malolos, he was the Auxiliary Bishop of Cebu from 2015 to 2019 and the Titular Bishop of Gisipa.