Conservation is to be “based on a respect for the existing fabric, use, associations and meanings” and “a cautious approach of changing as much as necessary but as little as possible.” At Humayun’s Tomb, the “cautious approach” required “necessary” removal of inappropriate 20th-century alterations—the million kilos of concrete laid on the roof and the almost 200,000 square feet of cement plaster.

The conservation effort at Humayun’s Tomb included “all efforts to...retain its value and significance, its authenticity and integrity...and to sustain a truthful representation of its original/ historic appearance”, with the purpose for each architectural element being “to ensure that the monument is kept in its original state or... restored to an earlier known state...”

Preservation, as the name implies, is only understood to mean effort aimed at "maintaining a place in its existing state and retarding deterioration."

The conservation effort at Humayun’s Tomb has aimed at ensuring preservation of all original fabric, especially any materials such as stonework with mason marks (even if in a poor state of preservation) and ceramic tiles that have remained on the canopies, even if these have lost their fragile layer of glaze and only the base of the Mughal-era tile remains. To ensure preservation, 20th-century alterations seen to be accelerating decay and obscuring original material were consistently and carefully removed and replaced with traditional materials.

A conservation action, globally recognized to be just as valid as preservation, restoration is described as "bringing back the monument or any part thereof, as nearly as possible, to an earlier known state or condition".

The documentation and archival research at Humayun’s Tomb revealed that architectural details in several parts of the building had been inappropriately altered in the 20th century, in a manner that would not be acceptable today. For the tilework on the canopies and the incised plaster on the facade of the ground level arcade, original patterns could be discerned on careful documentation. In both these cases, following widespread consultation, it was agreed to restore the tiles and the ornamental incised plasterwork respectively, matching the original, upon removing 20th-century cement layers. This restoration, based on "sufficient evidence of an earlier state of the fabric"20, allowed us to “reveal culturally significant aspects of the place."

Reconstruction, or to ‘rebuild in the original form’, is often required as part of conservation action where through neglect, vandalism or structural failure significant building parts have collapsed.

Each of the garden tombs—Humayun’s Tomb, Isa Khan’s Tomb, Bu Halima’s Tomb, Nila Gumbad, Mirza Muzzafar Hussain’s Tomb, Unknown Mughal tomb–were enclosed within arcaded masonry walls. Though a significant architectural element critical to retain the cultural significance, portions of the enclosure walls of the Humayun’s Tomb garden, Nila Gumbad garden, Bu Halima garden had either collapsed or, in the case of 20th century, partially demolished. Since long stretches of these walls were still standing, there was “sufficient evidence to reproduce an earlier state of the fabric” and reconstruction of collapsed portions was carried out.

The conservation effort has strictly conformed to the belief that “changes to a place should not distort the physical or other evidence it provides, nor be based on conjecture".

At Humayun’s Tomb, past interventions have on occasion even obliterated evidence of original architectural elements. For instance, while it is recorded in ASI publications that the walls of the principal tomb chamber were originally adorned with glazed ceramic tiles, all remaining fragments seem to have been removed in the mid-20thcentury possibly to achieve a clean appearance. No restoration of tilework was undertaken on the tomb chamber as conjecture would have required arriving at patterns, colours and placement of the tiles— none of which was known or documented.

The UNESCO statement on integrity for Humayun’s Tomb notes, “The tombs in the complex have been respected throughout their history and so have retained original form and purpose intact. Recent conservation works, that have followed the urban landscape approach, have been aimed at preserving this character and ensured the preservation of the physical fabric, enhancing its significance while reviving living building craft traditions used by the Mughal builders”. To ensure integrity, UNESCO in 2015 and 2016 consented to include nine 16th-century garden tombs, such as the Sundar Burj, Sundarwala Mahal and Unknown Mughal tomb within the expanse of the World Heritage Site property.

India boasts of a living building craft tradition that has managed to survive uninterrupted to the present day with craftsmen—stone carvers, masons, plasterers, ironsmiths, carpenters— all using tools, techniques and materials in the manner used by the 16th-century Mughal builders. Since 2007, use of these craft skills at Humayun’s Tomb has been appreciated. UNESCO has recognized that the repair interventions on the Tomb have been minimal and the aim has been to recover authenticity especially, by removal of 20th-century materials. To ensure authenticity of material, conservation works employed lime mortar for which lump lime was slaked on site and kept soaked for at least three weeks prior to preparation of mortar in the traditional lime wheel.

As with similar cases worldwide, repairs carried out to India’s monuments in the 20th century employed newly invented materials that only accelerated deterioration and disfigured historical architectural character. Soon, it was realized that modern materials such as cement caused damage to monuments built with traditional materials.

For the Humayun’s Tomb conservation, the conservation plan prepared at the onset outlined the intention to depend on master craftsmen not only to implement the conservation works but also be part of the decision-making systems established to plan for this large scale conservation effort. Hand-chiselling, rather than using machine tools, allows the finish to match the original and eventually have similar patina. Conservation project was used as a training platform with over 200 conservation professionals attending training workshops led by experts.