Adalbert I of Saarbrücken (? - 23 June 1137) was the Archbishop of Mainz from 1111 until 1137.

Adalbert was a son of Count Sigebert I of Saarbrücken. Adalbert supported Henry V against his father Emperor Henry IV, and on 14 February 1106 Adalbert is mentioned as being Henry V's chancellor. After the death of Ruthard, the Archbishop of Mainz, Adalbert was appointed the Archbishop in 1110 during the Investiture Controversy. It was not until the following year on the 15th of August that Adalbert received the mitre and staff, and not until 11 December that he was confirmed. The King and Pope Paschal II arranged a secret deal in February 1111 whereby the Emperor renounced the right of investiture of bishops and all invested bishops had to forfeit all rights, lands and privileges granted by the kings back to them. Adalbert rebelled with the other prince-bishops against the measure.

The king and pope entered negotiations again, however Paschal II cancelled it with the exception of the King's renunciation of investiture. Thus Henry V took him prisoner with Adalbert ruling the church in his stead, and he was released only after he confirmed the right of Henry to investiture and crowned him Holy Roman Emperor. Although the peace was short-lived, Adalbert used it in 1112 to ally with the forces led by Lothar of Supplinburg opposed to Henry V. It is unclear why Adalbert changed sides, however it might have been to try and secure more power in the Empire. Henry V hesitated before capturing Adalbert and imprisoning him in Burg Trifels in 1112, but Adalbert was released in 1115 after the citizens of Mainz rebelled for three years.

In 1119 and 1122, Adalbert rewarded the city of Mainz by granting it immunity from foreign taxes and courts, and various liberties. In 1119 Adalbert was appointed the papal legate for Germany, and Pope Callixtus II ordered him to work for peace between the church and state. This was decided on 23 September 1122 with the Concordat of Worms, which stripped the emperor of the right of investiture and rebuilt the church in Germany. In 1125 he prevented Duke Frederick II of Swabia from being elected Emperor, but was foiled in his designs by the surprise election of Lothar of Supplinburg, Duke of Saxony, who voted for himself. This resulted in the growing power of the Hohenstauffens to become hostile to Adalbert. In the schism of 1130 Adalbert was at first reserved before joining the other German bishops in support of Pope Innocent II.

Adalbert died in Mainz in 1137 and was buried in Mainz Cathedral.

Preceded by:

Adalbert I of Saabrücken

Succeeded by:

Ruthard Archbishop of Mainz
1111 - 1137
Adalbert II of Saarbrücken