The Temple of Hadrian (Templum Divus Hadrianus, also Hadrianeum) is an ancient Roman structure on the Campus Martius in Rome, Italy, dedicated to the deified emperor Hadrian by his adoptive son and successor Antoninus Pius in 145 CE. This temple was previously known as the Basilica of Neptune but has since been properly attributed as the Temple of Hadrian completed under Antoninus Pius. With one cella wall and eleven columns from the external colonnade surviving, the remains of the temple have been incorporated into a later building in the Piazza di Pietra (Piazza of Stone – derived from use of the temple's stones to build the piazza), whereby its facade, alongside the architrave which was reconstructed later on, was incorporated into a 17th-century papal palace by Carlo Fontana, now occupied by Rome's Chamber of commerce. While only part of the structure remains, excavations and scholarship have provided us with information regarding its construction techniques and stylistic influences, helping us recreate the building dynamics and significance of the Temple of Hadrian in Imperial Rome.

The emperor Hadrian died in 138 C.E. and his successor Antoninus Pius dedicated this temple in his name almost a decade later in 145 C.E. Although there is no surviving inscription to identify it as a temple to Hadrian, there was an inscription dedicated to him by his successor Antoninus Pius which was listed in the Regionary Catalogues amidst other Hadrianic dynastic monuments between the Pantheon and the Via del Corso.

There was apparently another major temple precinct located to the west, perhaps of Matidia and Marciana, Hadrian's mother-in-law and her mother, Trajan's elder sister, both of whom were also deified after their deaths.

Antoninus Pius' reign may not have seen major stylistic innovations in the architectural programs at Rome, but he did see to the completion of buildings begun or intended by his late predecessor Hadrian.

The Temple of Deified Hadrian was located within the Campus Martius (The Field of Mars) in close proximity to the earlier Solarium Augusti and later constructed Column of Marcus Aurelius. In the Notitia it is also listed as located in Regio IX near the Baths of Alexander Severus and Agrippa. The temple of Matidia (Hadrian's mother-in-law) also likely stood just to the west of the Temple of Hadrian so it has further been argued for the presence of monumental entrances at both ends of the temple though the remains offer no confirmation. The temple itself also stood within a spacious precinct surrounded by a colonnade, parts of which were uncovered by Rodolfo Lanciani in his early excavations of the surrounding spaces.

Long ago both ends of the temple, as well as the other side, disappeared; all that remains are eleven fluted columns with Corinthian bases and capitals, as well as one side of the cella wall which was built into a nineteenth century palazzo that continues to house the Rome Borsa.

While the lower part of the original richly carved entablature survives, the rest was recorded in sixteenth-century drawings. In modern times, the entablature was largely repaired in stucco with the cornice so poorly restored that three different versions exist with only the central one resembling the original.

Traces of vaulting beneath the front steps also demonstrate that the temple originally faced East (towards the Corso) and likely had eight columns across the front, with thirteen down either side of the structure. These traces also consist of surviving remains of clamps which suggest pilasters were joined to the colonnade.