Delegation is giving specific tasks and responsibilities to someone else, usually a junior. For instance, if you are an office manager and part of your work is to put new names into a database, you could delegate that to a trainee. Executives are often advised to "learn to delegate" because it's easy to take on too much work rather than share the burden.
Decentralisation is on a much bigger scale. It means moving power and authority away from the centre (usually national government) and handing it over to bodies or organisations outside the centre, especially regional organisations. In politics, this might mean that an area of policy - social housing, for instance - that used to be decided by the national government, is now the responsibility of local government, local councils and so on. The verb "to decentralise" is also quite often used, as in "We need to decentralise decision-making."
Delegation is the act of assigning tasks that are regarding work and/or power to subordinate workers. It is basically the turning over of some kind of authoritative power and responsibility to another individual to perform certain predefined tasks. Delegation gives the power to a person to make all major decision pertaining to the given task. In essence, delegation is simply the shift of power to make decisions from one hierarchal level to another, usually a lower one. Delegation if not done effectively, is called as micromanagement, when the subordinate is overloaded with too much data to handle.
On the other hand, decentralization refers to the transfer of decision making authority to the different unit of an organization. It is basically the procedure of spreading out the decision making, getting it closer to the point of action. Basically, it is delegation on a larger level so as to disperse the work and give each unit its own freedom and authority, instead of there being one centralised entity to which everyone reports.
When we say decentralization, we mean that instead of performing all the activities in the head office, the activities are carried out in centers outside the head office and adopting a geographic structure. An example of this is the MNCs that have operations all over the world. Doing work in a single central location is not feasible so various regional centers or office are established that are a miniature replica of the head office and take responsibility of the operations in that region. These offices follow the same rules in regulations. On the other hand delegation means that you transfer some portion of the authority to those who are actually doing the work and increase their responsibility. The difference between delegation and decentralization is that decentralization talks about the work to be done and not the authority. It deals with who will do what and is more related to the actual structure of the organization as it separates the various units. On the other hand delegation is about authority and decision making and it just increases the span of the job.
Decentralization basically is the procedure of scattering decision-making closer to the position of service or action, where as Delegation is the handing over of a task to another person.
Delegation generally is the transferring of power and responsibility to another person to execute specific activities. It permits a subordinate to make assessments. Delegation if properly executed is not abdication. The reverse of effective delegation is known as micromanagement, where a manager supplies extra input. Decentralization takes place in a number of contexts like engineering, management science, political science, political economy, sociology and economics.
It is said Law and science is also highly decentralized human practices. There are severe examinations conducted on how causality as well as correlation of phenomenon can precisely be determined and agreed across an entire country.
Delegation is giving a junior manager portion of power on a venture while decentralisation is allowing sub-unit to take part in discision making of the venture.
