Why do I need one of these statements on my resume?
The Objective/Professional Summary is an introduction to you and the remainder of your resume. To omit it would give your readers an experience equivalent to starting to read a book from the middle.
Well, an objective statement tells the reader what you are looking for in a position. For example, if you're in finance or accounting, an objective statement would be something like "Financial Analyst position with focus on expense analysis". You can read more about writing an awesome Objective Statement by clicking here.
Whereas a Professional Summary Statement highlights you and your accomplishments in one sentence. For example, assuming we are sticking with the finance and accounting, your professional summary may say something like, "Detail-oriented accounting professional with over 5 years experience in Big 4 public accounting firm". You can learn more about how to write an awesome Professional Summary Statement by clicking here.
How do you decide?
An objective statement is much more easy to come up with than a professional summary. The objective outlines your goals and tells the reader that you're interested in them and why. If you are applying for an entry-level position, I would suggest using an objective statement. Also, if you are trying to change professions or don't have much specific, relevant work experience, I would also suggest using an objective statement. Let your reader know that you are ready and rarin' to go!
A professional summary statement tells the reader how awesome you are and how you could benefit their company. It puts more focus on their needs and is generally a better choice for more targeted positions. If someone is looking for a specific level of experience in a job posting, and you just happen to have it, tell them in your summary statement. If you have an impressive history in the industry or have all of the technical qualities that they are looking for, let your reader know!
