OB or Ob may refer to:
Obsessive–compulsive disorder (OCD) is a mental disorder where people feel the need to check things repeatedly, perform certain routines repeatedly (called "rituals"), or have certain thoughts repeatedly.
Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which may contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods.
Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.
Objectivism is a philosophical system developed by Russian American writer Ayn Rand (1905–1982). Rand first expressed Objectivism in her fiction, most notably The Fountainhead (1943) and Atlas Shrugged (1957), and later in non-fiction essays and books.
The observable universe is a spherical region of the Universe comprising all matter that can be observed from Earth at the present time, because light and other signals from these objects have had time to reach Earth since the beginning of the cosmological expansion.
Obesity in the United States has been increasingly cited as a major health issue in recent decades. While many industrialized countries have experienced similar increases, obesity rates in the United States are among the highest in the world.