Are you interviewing for a job or conducting an informational interview to explore a career possibility? When it comes to interviewing, there's truth in that old adage, "You never get a second chance to make a good first impression". Just how long do you have to make that first impression? Statistically about 10 seconds. That's the amount of time that the average person takes to make a first appraisal. Much of that impression is at a subconscious level, and almost all of it based on appearances since your dress and grooming are the first things people notice about you.
What is appropriate dress for an interview? Most professional job interviews call for wearing professional dress. Take cues from the work environment for variations on the professional dress theme. For example, a classic navy suit would be fine in a traditional office setting, while a softly tailored dress would be appropriate in the more informal environment of a social services agency. When in doubt about what to wear - dress up. Even if you know that the employee dress code is very casual, it's appropriate to dress professionally for an interview. You're not an employee until you're hired. On the other hand, informational interviews are considered less formal so business casual would be appropriate.
Whether it's a job interview, or an informational interview, be thoughtful in deciding on your interview look. You want to be remembered for what you say, not for what you wear. For suggestions on both professional dress and business casual, review the Professional Attire document, which includes photographs, on the CEC's Career Toolkit.