When it comes to communication channels and their richness, face-to-face meetings are the most effective. They provide immediate feedback, multiple cues such as body language and tone, language variety including stories and metaphors, and personal focus like eye contact and gestures. This makes them ideal for persuading and mobilizing small groups of people who are familiar and engaged with your cause. Video calls are also a rich channel, but lack some personal focus. They are suitable for informing, persuading, and mobilizing small to medium groups of people who are diverse and interested in your cause. Phone calls are moderately rich channels, allowing for feedback and language variety but lacking multiple cues and personal focus. They are appropriate for informing and persuading small to medium groups of people who are somewhat familiar and receptive to your cause. Emails, text messages, and social media posts are all lean channels that allow for minimal feedback and language variety, but lack multiple cues and personal focus. Emails are useful for informing and persuading large groups of people who are diverse and curious about your cause, while text messages can effectively inform and mobilize large groups of people who are familiar and committed to your cause. Social media posts can be used to inform and mobilize large groups of people who are diverse and supportive of your cause.