Satisfaction is a relationship between specific sentences and specific truth assignments. In Logic, we are usually more interested in properties and relationships of sentences that hold across all truth assignments. We begin this chapter with a look at logical properties of individual sentences (as opposed to relationships among sentences) - validity, contingency, and unsatisfiability. We then look at three types of logical relationship between sentences - logical entailment, logical equivalence, and logical consistency. We conclude with a discussion of the connections between the logical properties of individual sentences and logical relationships between sentences.