Sections 45 to 51 of the Evidence Act, 1872 deal with the opinions of third persons including experts.
| Section | Question before the Court | Whose opinion is relevant | Remarks |
| 45 | As to a point of – foreign law – science or art
- the identity of handwriting or finger impressions |
An expert or person specially skilled | |
| 46 | Facts, not otherwise relevant, are relevant if they support or are inconsistent with the opinions of experts, when such opinions are relevant. | ||
| 47 | If a document has been written or signed by the person by whom it is supposed to have been written or signed | Any person acquainted with the handwriting of the person by whom it is supposed to be written or signed because of having seen that person write, receiving a reply from him or a document habitually submitted in the course of business | If it is/is not the handwriting of the person by whom it is supposed to be written or signed |
| 47 A | As to a digital signature | Certifying Authority which has issued it | |
| 48 | As to a general custom or right including that of any considerable class of persons | Person likely to be aware of its existence | |
| 49 | The usages and tenets of any body of men or family, the constitution and government of any religious or charitable foundation, or the meaning of words or terms used in particular districts or by particular or by particular classes of people | Person who has special means of knowledge thereon | |
| 50 | The relationship of one person to another | The opinion expressed by conduct, as to the existence of such relationship, of any person who, as a member of the family or otherwise, has special means of knowledge on the subject | Such opinion shall not be sufficient to prove a marriage in proceedings under the India Divorce Act, 1869 or in prosecutions under Sections 494, 495, 497 or 498 of the IPC |
| 51 | Whenever the opinion of any living person is relevant, the grounds on which such opinion is based are also relevant. | ||
However, when it comes to experts, there are a number of other provisions in the Evidence Act which also deal with them. These provisions mention:
1. The opinions expressed in any treatise commonly offered for sale (Section 60)
2. Expert opinion as to the general result of a number of documents Section 65(g)
3. An expert refreshing his memory Section 159
It is also worth noting that unlike other witnesses, witnesses who are called to give expert testimony may be asked hypothetical questions.