From “Merit Badges“, in the Scouting.org Advancement and Awards pages:
You can learn about sports, crafts, science, trades, business, and future careers as you earn merit badges. There are more than 135 merit badges, and any Boy Scout or Varsity Scout, or any qualified Venturer or Sea Scout may earn any of these at any time.
Pick a Subject. Talk to your unit leader about your interests. Read the requirements of the merit badges you think might interest you, and pick one to earn. Your leader will give you the name of a person from a list of counselors. These individuals have special knowledge in their merit badge subjects and are interested in helping you.
Scout Buddy System. You must have another person with you at each meeting with the merit badge counselor. This person can be another Scout, your parents or guardian, a brother or sister, a relative, or a friend.
Call the Merit Badge Counselor. Get a signed Application for Merit Badge, No. 34124 or No. 34130, from your unit leader. Get in touch with the merit badge counselor and explain that you want to earn the badge. The counselor may ask to meet you to explain what is expected and to start helping you meet the requirements. You should also discuss work you have already started or possibly completed.
At the first meeting, you and your merit badge counselor will review and may start working on the requirements. In some cases, you may share the work you have already started or completed.
Unless otherwise specified, work on a requirement can be started at any time. Ask your counselor to help you learn the things you need to know or do. You should read the merit badge pamphlet on the subject. Many troops, schools, and public libraries have them.
Show Your Stuff. When you are ready, call the counselor again to make an appointment. When you go, take along the things you have made to meet the requirements. If they are too big to move, take pictures or have an adult tell in writing what you have done. The counselor will test you on each requirement to make sure you know your stuff and have done or can do the things required.
Get the Badge. When the counselor is satisfied you have met each requirement, he or she will sign your application. Give the signed application to your unit leader so your merit badge emblem can be secured for you.
The current Boy Scout Requirements book is available from your local Scouting merchandise distributor. It may also be ordered online at ScoutStuff.org.
Merit badge requirements are revised as needed to reflect updated information and technology. Click here to view new and recently revised merit badges.
Requirements. You are expected to meet the requirements as they are stated—no more and no less. You must do exactly what is stated in the requirements. If it says “show or demonstrate,” that is what you must do. Just telling about it isn’t enough. The same thing holds true for such words as “make,” “list,” “in the field,” and “collect,” “identify,” and “label.”
The requirements listed below are the current and official requirements of the Boy Scouts of America. Occasionally, the requirements will not match those in the printed Boy Scout Handbook, the annual Boy Scout Requirements book, or some merit badge pamphlets because of the timing of their printing schedules.
If a new edition of a merit badge pamphlet is introduced with updated requirements after the Boy Scout Requirements book has been released, a Scout who is starting the badge may choose to follow either set of requirements until the end of the year. At the start of the new year, Scouts who are beginning must use only the new requirements.
If a Scout has already started working on a merit badge when a new edition of the pamphlet is introduced, he may continue to use the same pamphlet and fulfill the requirements therein to earn the badge. He need not start over again with the new pamphlet and revised requirements.
There is no time limit for starting and completing a merit badge, but all work must be completed by the time a Scout turns 18.