For the sake of the pupil the number of technical and scientific terms has been reduced to a minimum. The language has been made as simple as possible and the problems made to hinge upon material already known, by hearsay at least, to the pupil. So far as consistent with a well-rounded course in the essentials of biological science, the interests of the children have been kept in the foreground. In a recent questionnaire sent out by the author and answered by over three thousand children studying biology in the secondary schools of Connecticut, Massachusetts, New Jersey, and New York by far the greatest number gave as the most interesting topics those relating to the care and functions of the human body and the control and betterment of the environment. As would be expected, boys have different biological interests from girls, and children in rural schools wish to study different topics from those in congested districts in large communities. The time has come when we must frankly recognize these interests and adapt the content of our courses in biology to interpret the _immediate_ world of the pupil. With this end in view the following pages have been written. This book shows boys and girls living in an urban community how they may best live within their own environment and how they may cooperate with the civic authorities for the betterment of their environment. A logical course is built up around the topics which appeal to the average normal boy or girl, topics given in a logical sequence so as to work out the solution of problems bearing on the ultimate problem of the entire course, that of preparation for citizenship in the largest sense.