After hours of reading and googling, I still do not really understand how boiling works. I have some questions: What I know is that boiling occurs when the vapor pressure is equal to the atmospheric pressure. But I thought that vapor pressure is the pressure exerted by the water vapor above a body of water. If the vapor is above the water surface, why are there bubbles in the body of water? The explanation I have is that there are some pockets in the body of water where the state has changed from liquid to gas state. When the temperature is high enough, the vapor pressure exerted by these gas pockets is high enough that it can expand to form bubbles. Is that correct? If that's correct, then shouldn't the correct definition for boiling be "when the vapor pressure is equal to the atmospheric pressure PLUS the pressure from the body of water"? Another complication is that two books stated specifically that the SATURATED vapor pressure is equal to the external pressure when boiling occurs. I don't understand why it has to be saturated vapor pressure, not just vapor pressure. Isn't it possible for the external pressure (including atmospheric pressure) to be lower than the saturated vapor pressure, so boiling can occur before the vapor pressure equals to the saturated vapor pressure? The third question is related to open systems. I read on the web that the saturated vapor pressure of water cannot ever be higher than the external pressure (including atmospheric pressure) for an OPEN SYSTEM. My guess is that if the saturated vapor pressure exceeds the atmospheric pressure, bubbles will form and burst on the surface, “releasing” that pressure. Is that correct? Thanks for reading, and if you find any mistakes in my thinking, please point them out; I'm always glad to learn.