It seems that these 2 functions are pretty similar. They have same signature (accepting `rx.functions.Func1&lt;? super T, ? extends Observable&lt;? extends R&gt;&gt; func`), and their marble diagrams look exactly same. Can&#39;t paste the pics here, but here&#39;s one for [concatMap][1], and here&#39;s one for [flatMap][2]. There seems to be some subtle difference in the description of resulting `Observable`, where one produced by `concatMap` contains items that result from concatinating resulting Observables, and the one produced by `flatMap` contains items that result from first merging the resulting Observables, and emitting the result of that merger.

However, this subtlety is totally unclear to me. Can anyone give a better explanation of this difference, and ideally give some examples illustrating this difference.

  [1]: http://netflix.github.io/RxJava/javadoc/rx/Observable.html#concatMap%28rx.functions.Func1%29 &quot;concatMap&quot;
  [2]: http://netflix.github.io/RxJava/javadoc/rx/Observable.html#flatMap%28rx.functions.Func1%29 &quot;flatMap&quot;

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What is the difference between concatMap and flatMap in RxJava