How to place two divs next to each other?

Having two divs, you could also use the display property:

#wrapper {
    border: 1px solid blue;
}
#div1 {
    display: inline-block;
    width:120px;
    height:120px;
    border: 1px solid red;
}
#div2 {
    display: inline-block;
    width:160px;
    height:160px;
    border: 1px solid green;
}

<div id="wrapper">
    <div id="div1">The two divs are</div>
    <div id="div2">next to each other.</div>
</div>

If div1 exceeds a certain height, div2 will be placed next to div1 at the bottom. To solve this, use vertical-align:top; on div2.

#wrapper {
    border: 1px solid blue;
}
#div1 {
    display: inline-block;
    width:120px;
    height:120px;
    border: 1px solid red;
}
#div2 {
    vertical-align:top;
    display: inline-block;
    width:160px;
    height:160px;
    border: 1px solid green;
}

<div id="wrapper">
    <div id="div1">The two divs are<br/><br/><br/><br/><br/><br/></div>
    <div id="div2">next to each other.</div>
</div>

jsFiddle for example 1.

jsFiddle for example 2.

Try to use flexbox model. It is easy and short to write.

Live Jsfiddle

CSS:

#wrapper {
  display: flex;
  border: 1px solid black;
}
#first {
    border: 1px solid red;
}
#second {
    border: 1px solid green;
}

default direction is row. So, it aligns next to each other inside the #wrapper. But it is not supported IE9 or less than that versions

You can sit elements next to each other by using the CSS float property:

#first {
float: left;
}
#second {
float: left;
}

You'd need to make sure that the wrapper div allows for the floating in terms of width, and margins etc are set correctly.

Float one or both inner divs.

Floating one div:

#wrapper {
    width: 500px;
    border: 1px solid black;
    overflow: hidden; /* will contain if #first is longer than #second */
}
#first {
    width: 300px;
    float:left; /* add this */
    border: 1px solid red;
}
#second {
    border: 1px solid green;
    overflow: hidden; /* if you don't want #second to wrap below #first */
}

or if you float both, you'll need to encourage the wrapper div to contain both the floated children, or it will think it's empty and not put the border around them

Floating both divs:

#wrapper {
    width: 500px;
    border: 1px solid black;
    overflow: hidden; /* add this to contain floated children */
}
#first {
    width: 300px;
    float:left; /* add this */
    border: 1px solid red;
}
#second {
    border: 1px solid green;
    float: left; /* add this */
}