Dear Aspirant,

Good question.

IES, IAS are both Union Government cadres for which exams are conducted by UPSC.

The Indian Economic Service (IES) is the administrative civil service under Grade A of the Central Civil Services of the executive branch of the Government of India.
Role of the service can be broadly categorized in terms of economic advice, economic administration, implementation of development policy and programmes, besides dealing with other areas such as economic reforms, regulation, price fixation, and monitoring and evaluation. In the rapidly globalizing environment, decision-making is increasingly guided by economic rationality. In view of the on-going reforms pursued by the Government, the role of IES officers has assumed much significance. Apart from the purely economic sectors, IES officers are making crucial contribution towards policy making in social sectors.

Candidates recommended for IES start their career as Assistant Director. The existing hierarchy in the service is as follows:

Higher Administrative Grade +(Principal/Chief Adviser, equivalent to the level of Secretary in the Government of India)
Higher Administrative Grade (Senior Economic Adviser/Senior Adviser, equivalent to the level of Addl. Secretary in the Government of India)
Senior Administrative Grade (Economic Adviser/Adviser, equivalent to the level of Joint Secretary in the Government of India)
Non-Functional Selection Grade (Director/Additional Economic Adviser, equivalent to the level of Director in the Government of India)
Junior Administrative Grade (Joint Director/Deputy Economic Adviser/Deputy Adviser, equivalent to the level of Deputy Secretary in the Government of India)
Senior Time Scale (Deputy Director/Assistant Adviser/Assistant Commissioner/Senior Research Officer, equivalent to the level of Under Secretary in the Government of India)
Junior Time Scale (Assistant Director)

The Indian Administrative Service (abbreviated as IAS) is the premier administrative civil service of the Government of India. IAS officers hold key and strategic positions in the Union Government, States and public-sector undertakings.

Along with the Indian police and forest services, the IAS is one of the three All India Services-its cadre can be employed by both - the Union Government and the States.

A civil servant is responsible for the law and order and general administration in the area under his work. Typically the functions of an IAS officer are as follows:

To handle the daily affairs of the government, including framing and implementation of policy in consultation with the minister-in-charge of the concerned ministry.
Implementation of policy requires supervision.
Implementation requires travelling to places where the policies are being implemented.
Implementation also includes expenditure of public funds which again requires personal supervision as the officers are answerable to the Parliament and State Legislature for any irregularities that may occur.
In the process of policy formulation and decision making, officers at various levels like joint secretary, deputy secretary make their contributions and the final shape to the policy is given or a final decision is taken with the concurrence of the minister concerned or the cabinet depending upon the gravity of the issue.

Best wishes

Is the exam of IES based on aptitude ?

Any competitive exam is highly based on Aptitude / IQ