What is IAS Exam?
Indian Administrative Service (IAS) was formerly known as Imperial Civil Service (ICS) is the Civil Services Examination and one of the toughest competitive exams in India. It is conducted by the Union Public Service Commission for the recruitment of officers for the All India Administrative Civil Service.

About IAS:
Founded:

1858 (as Imperial Civil Service)
January 26, 1950 (as Indian Administrative Service)
The Indian Administrative Service is the premier administrative civil service of the Government of India. HIerarchy-wise, IAS is the highest administrative post among the 24 services like IPS, IFS etc. IAS is the permanent bureaucracy in India and forms a part of the executive branch. It is one of the three All India Services, its cadre can be employed by both the Union Government, the State Governments and public-sector undertakings.

Being an IAS Officer
An IAS officer is given administrative command of an entire district as a District Collector. IAS officers also represent Government of India at international level in bilateral and multilateral negotiations.

Eligibility Criteria
Nationality:

Candidate must be a citizen of India
Candidate must be a citizen of Nepal or a subject of Bhutan
Candidate must be a Tibetan Refugee who came to India before January 1, 1962, to be settled permanently in India
Candidate must be person of Indian Origin who has migrated from Ethiopia, Kenya, Malawi, Myanmar, Pakistan, Sri Lanka, Tanzania, Uganda, Vietnam, Zaire, or Zambia with an intention of permanently settling in India
Educational Qualification:
Candidate applying for civil service exams is required to fulfill the following criteria:
Candidate must hold a Bachelor’s Degree from any of the recognized universities
Candidates who have appeared for the qualifying examination and are awaiting results or those who are yet to appear for the qualifying examination are also eligible for the Preliminary Examination. Such candidates have to produce proof of passing the said examination along with the application for the Main Examination
Candidates with professional and technical qualifications recognized by the Government or its equivalent are also eligible to apply
Candidates who have passed the final year of MBBS or any Medical Examination but are yet to complete the internship can also appear for the Main Examination. However, they must submit a certificate from the concerned University that they have passed the final professional medical examination
Age Limit :
A candidate should be minimum of 21 years and maximum 32 years old as on August 01, 2018. But he/she must have been born not earlier than August 02, 1986 and not later than August 01, 1997. Necessary action will take to make corresponding changes in respective Rules/Regulations pertaining to various services.

The upper age limit prescribed above is relaxable for the following candidates:

5 Years – Scheduled Caste/ Scheduled Tribe (SC/ST)
3 Years – Other Backward Classes (OBC)
3 Years – Defence Services personnel
5 Years – ex-servicemen including Commissioned Officers and ECOs/SSCOs who have rendered at least 5 years Military Service as on August 01, 2018
5 Years in the case of ECOs/SSCOs
10 Years – Blind, deaf-mute, and orthopedically handicapped persons
5 Years – In the case of ECOs/SSCOs who have completed an initial period of assignment of five years of Military Service as on 1st August, 2018 and whose assignment has been extended beyond five years and in whose case the Ministry of Defence issues a certificate that they can apply for civil employment and that they will be released on three months’ notice on selection from the date of receipt of offer of appointment
Number of attempts:
Restriction on the maximum number of attempts is effective since 1984:

For General Candidates: 7 attempts (Up to 32 Years)
Scheduled Caste and Scheduled Tribe Candidates (SC/ST): No Limits (Up to 37 Years)
Other Backward Classes (OBC): 9 attempts (Up to 35 Years)
Physically handicapped- 9 attempts for general and OBC, while unlimited for SC/ST
Roles and Responsibilities
The role of IAS officers is very venerable, demands a great deal of responsibility and reverence. It is also important that an officer is physically and mentally fit and healthy to handle the work pressure without giving in. The following are the roles and responsibilities that an IAS officer is deputed:

Handling affairs of government that involve framing and implementation of policy in consultation with the concerned Minister
Implementing policies through supervision and also traveling to the places where the approved policies will be implemented
Implementing policies comprises disbursement of funds through personal supervision
Answerable to the Parliament and State Legislatures for any violation of rules while on duty
Functions and responsibilities differ at different levels of career
Initially, IAS officers join the state administration at the sub-divisional level, resuming their services as sub-divisional magistrates, and look after law and order, general administration and development work in the area assigned to them
The post of the District Officer also known as District Magistrate, District Collector or Deputy Commissioner is the highly respected and responsible post the IAS officers enjoy
At the district level, an IAS officer deals with district affairs, including implementation of developmental programs
The officers may also be appointed in the State Secretariat or they may serve as Heads of Departments or in Public Sector Undertakings
They may serve in different positions from the State to the Centre and vice versa. This happens through deputation.
At the Centre, IAS officers serve at the highest position as the Cabinet Secretaries, Secretaries/Additional Secretaries, Joint Secretaries, Directors, Deputy Secretaries and Under Secretaries. They are appointed to these posts based on seniority.
At the Centre, the IAS officers play a key role in formulation and implementation of policies related to a particular area; for instance, finance, commerce, etc.
During formulation of a policy and decision making, IAS officers serving at different levels i.e. joint secretary, deputy secretary give their valuable inputs
The policy takes its final shape through a final decision the minister concerned or the cabinet, depending on the seriousness of the situation
Contents from: https://www.careerindia.com/upsc/ias-exam-e1.html