How to remove button shadow (android)

A simpler way to do is adding this tag to your button:

android:stateListAnimator="@null"

though it requires API level 21 or more..

Another alternative is to add

style="?android:attr/borderlessButtonStyle"

to your Button xml as documented here http://developer.android.com/guide/topics/ui/controls/button.html

An example would be

<Button
android:id="@+id/button_send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_send"
android:onClick="sendMessage"
style="?android:attr/borderlessButtonStyle" />